Objective: To study and compare in healthy subjects and patients with Parkinson´s disease (PD) the destabilizing force needed to reach the limit of stability (LoS), the displacements of the center of pressure (CoP) and the postural stabilizing strategies while performing the pull test (PT).

Background: The PT is the only item that assesses postural stability in the motor part of the Unified Parkinson Disease Rating Scale. The force needed to perform the PT is a recognized source of variability which has not been analyzed quantitatively.

Methods: Healthy subjects and PD patients H-Y stage I, II and III were studied. Using a pull apparatus, sequential and sudden pulls were applied in an anterior-posterior direction, with progressive increase in the pull-force until the subject had to step back (LoS). During the procedure, subjects stood on a posturographic platform and electromyographic (EMG) recordings were obtained from anterior and posterior leg and trunk muscles.

Results: 64 healthy subjects and 32 PD, 22 H-Y stages I-II and 10 H-Y stage III, who executed a total of 476 tests were analyzed. Mean pull-force to LoS in controls was 98,8N(Newtons), 70,5N in PD H-Y I-II and 37,7N in PD H-Y III. Pull-force was correlated with age (p<0,001) and sex (p<0,001). Multivariant analysis including age and sex showed no significant difference in pull-force between controls and PD H-Y I-II, but it was 30,8N lower in PD H-Y III (p=0,046). In PD group, the pull-force diminished with the advance in H-Y stage (p=0,015) and with the presence of self-reported falls (p=0,011). Posturography and EMG showed in PD an increased CoP posterior velocity (p=0,001), CoP displacement areas (p=0,044) and longer latencies in muscular activation (p<0,001). PD H-Y III registered greater CoP displacement areas than PD H-Y I-II (p=0,01). A combination of ankle and hip strategies was predominant to maintain balance in controls and PD.

Conclusions: In the Pull Test, the perturbation force needed to reach the LoS is inferior in PD patients with postural instability (H-Y III) than controls and early stages of PD (H-Y I-II). In addition, PD group showed longer latencies, increased CoP posterior velocity and CoP displacement areas, especially in PD H-Y III. These results indicate that the pull-force should be a parameter to consider in the evaluation of PT as its lower values may be associated to postural instability.

References: 1. Fahn S, Elton R, members of the UPDRS Development Committee. Unified Parkinson’s Disease Rating Scale. In: Fahn S, Marsden CD, Calne D, Goldstein M, eds. Recent Developments in Parkinson’s Disease, vol. 2. Florham Park, NJ: Macmillan Healthcare Information; 1987. p 153–163,293–304.

2. R.P. Munhoz, J.-Y. Li, M. Kurtinecz, P. Piboolnurak, A. Constantino, S. Fahn,  A.E. Lang. Evaluation of the pull test technique in assessing postural instability in Parkinson’s disease, Neurology; 62:125–127, 2004.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/the-pull-test-in-healthy-subjects-and-parkinsons-disease-quantitative-pull-force-measure-postugraphic-and-electromyographic-analysis/