Original articlePostural control of the trunk during unstable sitting in Parkinson's disease
Introduction
Postural instability and falls are common in Parkinson's disease (PD) [1], [2]. In a recent prospective study over 6 months, about 50% of the PD patients fell, compared to about 15% of healthy elderly subjects [3]. A fall can have serious consequences. It can lead to injuries, of which hip fractures are most serious. In addition, corollaries of a fall-event, such as fear of falling, immobility and functional impairments may lead to serious limitations of activities and participation [4].
Almost 75% of falls in PD occur due to the inability to control the mass of the body during execution of activities of daily living, such as turning around, standing up and bending forward [3]. It is believed that adequate control of trunk movements is very important for postural stability, as the upper body constitutes two-thirds of the total body weight [5]. Due to the heavy mass and its height above the ground, even small, uncoordinated movements of the trunk may increase the risk of balance loss and falls. Mounting evidence suggests that the trunk control is changed in PD patients [6], [7]. Recently, Adkin et al. [8] demonstrated that the amplitude of trunk sway measurements during standing can discriminate between healthy controls and PD patients with recent falls.
Only limited insight into the mechanisms underlying the control of the trunk can be gained by studying postural control during quiet stance. In standing, postural adjustments can be accomplished with a wide range of responses at the ankle, knee, hip and trunk joints independently, or combined [9], [10]. In quiet standing and after mild perturbations, ankle responses dominate balance control [11], [12] In sitting, postural control of the trunk can be studied without the influence of lower extremity responses. Several studies have used an unstable seat paradigm successfully to study postural control of the trunk in healthy and low back pain subjects [13], [14], [15]. With this method, the subjects are requested to maintain balance, while sitting on an inherently unstable hemisphere using only trunk movements.
In this exploratory study, we investigated whether PD patients show alterations in dynamic trunk control compared to healthy controls during unstable sitting. An additional aim was to study differences in trunk control between PD patients that have a history of falling (fallers), and PD patients that do not have a history of falling (non-fallers). Balance performance was quantified using endurance time (ET) and number of successful trials. In addition, standard measures of center of pressure (CoP) excursions and trunk angular deviations were calculated, as well as their frequency characteristics. We hypothesized that PD patients, and especially fallers would have decreased performance on the unstable seat compared to healthy controls. In addition, it was expected that CoP and trunk angle measures would show evidence of changes in dynamic balance control. Specifically, we anticipated increased CoP excursions related to postural instability, reduced angular deviations related to trunk stiffness, and reduced frequency content of CoP and trunk excursions related to slower trunk movements, between PD patients and controls, as well as between fallers and non-fallers.
Section snippets
Subjects
Sixteen PD patients (8 ♀, 8 ♂) and eight age-matched controls (4 ♀, 4 ♂) participated (Table 1). Eight patients had a history of falls, which was defined as at least two reported falls in the last 12 months. Subjects were excluded if they had other neurological, vascular, musculoskeletal and vestibular disorders that could impair balance control, or serious cognitive impairments. Patients were evaluated on the modified Hoehn and Yahr scale and the Unified Parkinson's Disease Rating scale
Results
The demographic characteristics were not significantly different between the three groups, nor were the Hoehn and Yahr and UPDRS scores different between the two patient groups (, see Table 1), confirming the comparability of the groups.
Discussion
As hypothesized, differences were observed in dynamic balance control of unstable sitting between PD patients and healthy controls. These differences did not only occur in ET and number of successful trials, but also in the amplitude of CoP excursions, trunk angular deviations and their frequency characteristics. The trends of increasing CoP excursions from healthy controls to PD patients non-susceptible for falling to patients who are at risk for falling suggest that increased postural
Conclusion
PD patients show definite alterations in trunk postural control compared to healthy controls. The current results corroborate and extend previous findings that pathological changes in trunk control are related to fall risk and postural instability.
Acknowledgements
The authors would like to thank the students Marjolijn Binnekade, Rebecca Baines and Martijn Rhebergen for help with the experiments. This study was supported in part by Grant no. 2004/12 from the research institute MOVE of the VU University Medical Center.
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