Assessing muscle stiffness from quiet stance in Parkinson's disease

In previous studies, we developed a postural stiffness measure that is extr acted from foot center-of-pressure (COP) trajectories from quietly standing individuals and is based on an analytical mechanical model of posture cont rol. Here we apply this measure to patients with Parkinson's disease (PD). We correlated the postural stiffness measure with different clinical rating scales, obtained from patients. Kendall's rank correlation was highly sign ificant between the stiffness measure and rigidity, bradykinesia, posture i mpairment, gait, and leg agility, respectively, as rated by the Unified Par kinson's Disease Rating Scale. These results provide further evidence that a higher intrinsic muscle stiffness may contribute to the aforementioned cl inically defined symptoms. From a clinical standpoint, this work indicates that the proposed postural stiffness measure may be useful as an assessment tool for the evaluation of PD patients subsequent to pharmacological and s urgical treatment. (C) 1999 John Wiley & Sons, Inc.