Characterisation of foot clearance during gait in people with early Parkinson׳s disease: Deficits associated with a dual task
Introduction
Falls are a large public health issue placing considerable strain on the healthcare system with escalating costs of £4.6 billion/year in the UK alone (Age UK, 2010). It is estimated that one third of older adults (Department of Health, 2009) and two thirds of people with Parkinson׳s disease (PD) (Ashburn et al., 2001; Wood et al., 2002) fall every year, with the majority of falls resulting from a trip (Blake et al., 1988; Gazibara et al., 2014). Tripping occurs when there is an unanticipated foot contact with the ground and a fall ensues when balance recovery is insufficient. Inadequate limb elevation (specifically foot clearance) during gait is an under-reported and poorly understood factor likely contributing to the high prevalence of trips in older adults and PD. This is surprising when considering that a high proportion of indoor (14.3%) and outdoor (66%) falls by PD are the result of a trip or slip (Gazibara et al., 2014). Consequently, understanding the mechanisms underpinning trip risk is of importance and profiling foot clearance may inform the development of interventions to reduce trip risk (Lai et al., 2012; Hamacher et al., 2014).
Foot clearance during swing follows a typical pattern whereby heel displacement progresses both anteriorly and vertically until a peak (~25 cm in the young (Winter, 1992)) is reached mid-swing. Toe clearance is often biphasic with a peak in early and late swing. One of the gait events posing the greatest risk for tripping is considered to occur mid-swing, when the anterior velocity of the toe reaches a peak and a minimum clearance of ~1.5 cm is achieved in young adults (Winter, 1992). Further work is required to establish whether other foot clearance events may be used to distinguish between clinical groups to evaluate falls risk. Unanticipated contact of the toe with either the ground/environmental object may also occur during early swing, when the foot is plantarflexed and accelerating to facilitate limb elevation. Conversely, unanticipated contact of the heel with the ground/environmental object may occur during late swing when the foot is dorsiflexed and decelerating in preparation for foot contact. Limited evidence suggests that foot clearance is reduced in established PD when compared to controls and worsens with disease severity although these studies included small samples (n=10–21)(Knutsson, 1972; Cho et al., 2010) and require affirming with larger cohorts.
Online cognitive processing and execution of motor actions often occur concurrently during real world locomotion and therefore constructing assessments using a dual task paradigm offers a more ecologically valid evaluation of gait. Under dual task conditions (visual reaction time), no significant difference in minimum toe clearance was observed for young and old men (Sparrow et al., 2008). However these changes were observed whilst walking on a treadmill which does not allow for the natural acceleration and deceleration inherent in bipedal gait. Conversely, alterations in foot clearance appear to be exacerbated most with the addition of a secondary cognitive task (as opposed to a secondary motor task) with the mean minimum toe clearance for some individuals as low as 2 mm when required to answer standardised questions whilst walking compared to single task walking or completing an additional motor task when the mean minimum toe clearance was >4 mm (Schulz et al., 2010). Considering the motor (Morris et al., 1994; Jankovic, 2008) and non-motor (cognitive) (Chaudhuri et al., 2006; Hou and Lai, 2007; Poewe, 2008; Park and Stacy, 2009) symptoms of PD, gaps in our knowledge surrounding the influence of a dual task on foot clearance exist. Trip risk may be further exacerbated under dual task, particularly tasks that challenge cognitive reserve, although this remains unknown.
Characteristics of foot clearance have been associated with temporal-spatial components of gait in young (Osaki et al., 2007; Cho et al., 2010) and older adults (Sparrow et al., 2008). Slower gait velocity, a shorter step length and increased asymmetry and variability of temporal-spatial gait parameters are recognised gait deficits in early (Galna et al., 2014) and established (Morris et al., 1996; Hausdorff et al., 1998; Yogev et al., 2007; Roiz et al., 2010; Hass et al., 2012) PD. Slower velocities in PD are thought to be a product of reduced step length rather than altered cadence which may be modulated to meet increasing velocity demands (Morris et al., 1994). Holistically, anterior progression during gait (velocity) is a product of temporal (timing) and spatial (distance) control. A slowness (bradykinesia) and reduced magnitude of movement (hypokinesia) are hallmark impairments associated with PD gait. The association between temporal (step time), spatial (step length) and these factors combined (gait velocity) and foot clearance in PD is unknown and understanding this association may help to tailor therapeutic interventions targeting fall prevention in PD.
The aims of this exploratory study were to evaluate if foot clearance is: 1) altered in early PD compared to controls; 2) negatively influenced by a concurrent cognitive (dual) task; and 3) associated with altered temporal-spatial components of gait in PD. To this end, characterisation of foot clearance during single and dual task gait in early PD will serve as a baseline from which disease progression and falls risk may be estimated longitudinally. Based on the limited empirical evidence available, it was hypothesised that: i) foot clearance would be reduced in the PD cohort compared to controls; ii) the addition of a dual (cognitive) task would have a negative influence on temporal-spatial characteristics of gait and foot clearance in both groups, with larger changes in PD; and iii) foot clearance would be largely dependent on both temporal and spatial components of gait.
Section snippets
Participants
Participants were recruited into the ICICLE-GAIT study within 4 months of diagnosis. This is a collaborative study with ICICLE-PD, an incident cohort study (Incidence of Cognitive Impairment in Cohorts with Longitudinal Evaluation – Parkinson׳s disease) conducted between June 2009 and December 2011 (Khoo et al., 2013; Yarnall et al., 2014). ICICLE-GAIT recruited a subset of the cohort at the same time point. A diagnosis of idiopathic PD was given by a Movement Disorders Specialist according to
Results
No significant differences existed between the groups for age, height or mass for either the single or dual task cohorts (Table 1). Under single task conditions, a total of 4256 steps were analysed (Control n=2320, PD n=1936) and 2082 steps for dual task (Control n=1194, PD n=888).
Discussion
To our knowledge, this exploratory study is the largest to characterise foot clearance during overground gait using a broad range of measures in a large cohort of early PD and explore the effects of a concurrent cognitive (dual) task. We have demonstrated that foot clearance is altered even in the early clinical stages of PD and is adversely affected by a dual (cognitive) task in both older adults and PD.
Conclusions
Distinct differences in foot clearance during gait between older adults and PD were observed and these deviations were most notable under dual task. Further work is required to understand the kinematic co-ordination underpinning the presence of unimodal toe distributions. Interventions that improve gait velocity and step length will likely improve foot clearance in PD. Trajectory gradients may provide a unique insight into altered foot trajectories in PD and may help inform the design of falls
Conflict of interest statement
The authors have no financial or personal conflicts of interest to declare.
Acknowledgements
ICICLE-GAIT is supported by the National Institute for Health Research (NIHR) Newcastle Biomedical Research Unit based at Newcastle upon Tyne Hospitals NHS Foundation Trust and Newcastle University. ICICLE-PD is supported by Parkinson׳s UK. The research was also supported by NIHR Newcastle CRF Infrastructure funding. The views expressed are those of the authors and not necessarily those of the NHS, the NIHR, or the Department of Health.
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