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Accuracy of Digitization Using Automated and Manual Methods

DJ Wilson, PhD, is Clinical Assistant Professor, Gait Laboratory, Department of Physical Medicine and Rehabilitation–DC 0046.00, Howard A Rusk Rehabilitation Center, University of Missouri–Columbia, One Hospital Dr, Columbia, MO 65212 (USA) (dan_wilson{at}pmr.missouri.edu). Address all correspondence to Dr Wilson
BK Smith, JK Gibson, PT, OCS, BK Choe, BC Gaba, and JT Voelz were graduate students, Department of Health and Exercise Sciences, University of Missouri–Columbia, at the time this study was conducted

Background and Purpose. Computerized 3-dimensional (3-D) motion measurement systems are used by those interested in human motion. The purposes of this study were (1) to determine the limits of accuracy in determining intersegmental angles during pendular motion at varying speeds and (2) to determine changes in accuracy introduced by autodigitization and digitization by experienced manual raters. Methods. Angular speed of a T-shaped pendulum was systematically increased by releasing the pendulum from 4 angles (0° [no movement], 45°, 90°, and 120°). Twelve reference angles calculated from markers placed on the pendulum were estimated over 20 frames for 10 trials at each release position. Results. Mean errors across trials and frames for intersegmental angles reconstructed by a 3-D motion measurement system were within ±1 degree across all release positions. An analysis of variance and a post hocTukey test revealed that the mean error for the autodigitized trials was larger than that for the manually digitized trials. For the autodigitized trials, the static trials (release position=0°) produced less mean error than the trials with movement produced. The ICCs showed a high degree of consistency among all raters, ranging from .707 to .999. Conclusion and Discussion. Our findings support the conclusion that under carefully controlled conditions, a 3-D motion measurement system can produce clinically acceptable measurements of accuracy across a range of angular speeds. Furthermore, acceptable accuracy is possible regardless of the digitization method.

Key Words: Accuracy • Digitization • Kinematics • Videotape analysis

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