Videographic Determination of Instantaneous Center of Rotation Using a Hinge Joint Model

John H. Hollman, Robert H. Deusinger

There are many 2-dimensional and 3-dimensional kinematic measuring systems available on the commercial market for studying and analyzing human movement. Although each system gathers data by use of different technologies, the systems use similar mathematical methods to generate 2- or 3-dimensional coordinates of surface markers reconstructed from a spatial calibration of multiple planar views. The reconstructed marker coordinates are the basis for deriving kinematic parameters of displacement, velocity, and acceleration used to describe human movement. Because numerous motion analysis systems exist, considerable literature exists addressing the accuracy and application of such systems, primarily in relation to measurement of static or dynamic linear and angular segmental variables applied to studies of human movement. It is possible to assess intrinsic knee joint dysfunction such as ligamentous instability or degenerative pathology by measuring the instantaneous center of rotation (ICR) derived from segmental kinematic data. During planar motion between any two segments and at each instant through the joint's excursion, there exists a unique point, the ICR, at which the instantaneous velocity is zero and about which pure rotation of one segment relative to the other occurs. The ICR is stationary through the joint's range of motion with a true hinge joint. Most human joints, however, are not true hinge joints; the ICR moves during a joint's excursion, creating a pathway of the instantaneous center of rotation, or PICR. Location of the PICR relative to joint surfaces can be used to infer joint function. Information concerning joint surface velocity, joint surface compression and distraction, and the rolling/gliding mechanism can also be inferred from the PICR This technical report presents methodology using videographic motion analysis to calculate 2-dimensional ICR. It represents an initial step in developing a valid and reliable method for determining PICR of the knee joint during dynamic activities. We intend to assess the accuracy of videographic methodology for measuring ICR under the ideal conditions of a true hinge joint model.

J Orthop Sports Phys Ther. 1999;29(8):463-469.

Key Words: kinematic measurement systems, motion analysis, ICR, PICR

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