The Volume of Motion: Introduction, Derivation, and an Application Comparing Various Spinal Fixation Devices

[+] Author and Article Information
J. J. Crisco

Department of Engineering & Applied Science, Yale University, and Department of Orthopaedics & Rehabilitation, Yale University School of Medicine, New Haven, CT 06510

J Biomech Eng 115(1), 43-46 (Feb 01, 1993) (4 pages) doi:10.1115/1.2895469 History: Received February 01, 1991; Revised April 22, 1992; Online March 17, 2008


Range of motion (ROM), the displacement between two limits, is one of the most common parameters used to describe joint kinematics. The ROM is a one-dimensional parameter, although the motion at many normal and pathological joints is three-dimensional. Certainly, the ROM yields vital information, but an overall measure of the three-dimensional mobility at a joint may also be useful. The volume of motion (VOM) is such a measure. The translational VOM is the volume defined by all possible ROMs of a point on a rigid body. The rotational VOM, although its interpretation is not as tangible as the translational VOM, is a measure of the three-dimensional rotational mobility of a rigid body. The magnitude of the VOM is proportional to mobility; the VOM is a scaler, which does not contain any directional information. Experimental determination of the VOM is not practical since it would require applying loads in an infinite number of directions. The mathematical derivation given here allows the VOM to be calculated, with the assumption of conservative elasticity, from the resultant displacements of three distinct load vectors of equal magnitude. An example of the VOM is presented in the comparison of the biomechanical stabilizing potential of various spinal fixation devices.

Copyright © 1993 by The American Society of Mechanical Engineers
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