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Vol. 37 No. 4, July/August 2000

Quantifying ataxia: Ideal trajectory analysis-- A Technical Note

Michael D. McPartland, PhD; David E. Krebs, PhD, PT; Conrad Wall III, PhD

Harvard Medical School, Department of Orthopaedics, Massachusetts General Hospital Biomotion Laboratory, Boston, MA 02114; MGH Institute of Health Professions, Boston, MA 02114; Harvard Medical School, Department of Otolaryngology, Jenks Vestibular Laboratory, Boston, MA 02114; Massachusetts Eye and Ear Infirmary, 243 Charles Street, Boston, MA 02114

Abstract — We describe a quantitative method to assess repeated stair stepping stability. In both the mediolateral (ML) and anterio-posterior (AP) directions, the trajectory of the subject's center of mass (COM) was compared to an ideal sinusoid. The two identified sinusoids were unique in each direction but coupled. Two dimensionless numbers--the mediolateral instability index (IML) and AP instability index (IAP)--were calculated using the COM trajectory and ideal sinusoids for each subject with larger index values resulting from less stable performance. The COM trajectories of nine nonimpaired controls and six patients diagnosed with unilateral or bilateral vestibular labyrinth hypofunction were analyzed. The average IML and IAP values of labyrinth disorder patients were respectively 127% and 119% greater than those of controls (p<0.014 and 0.006, respectively), indicating that the ideal trajectory analysis distinguishes persons with labyrinth disorder from those without. The COM trajectories also identify movement inefficiencies attributable to vestibulopathy.

Key words: ataxia, balance assessment, body sway, stability, vestibular subject

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