Motor stability evaluation in elderly subjects through instrumental stability measures and clinical rating scales

Main topics: Experimental studies in human movement science; Movement deviation indexes Introduction and aim: Falls in the elderly represent a major community and public health problem, with large clinical and economic consequences [1]. The understanding of locomotor stability is a critical issue in clinical assessment procedures. Clinicians typically use clinical rating scales of motor function tests for fall risk assessment purposes. However, this approach highly relies on the clinician's subjective judgement [2]. Variability and stability measurements of stride time and trunk accelerations during gait resulted promising in the assessment of gait stability and fall risk in healthy elderly subjects [3] and could lead to a more reliable and objective quantification of motor function, potentially representing a valid and objective complement to clinical rating scales. For an effective exploitation in clinical practice, the association between stability measures and clinical scales has to be assessed. The aim of the present study is the assessment of the relationship between instrumental variability and stability measures based on trunk accelerations during gait and some widely used clinical rating scales. Patients/materials and methods: Seventy community dwelling old adults (35 males and 35 females, 76 ± 7 years, 76 ± 13 kg, 168 ± 9 cm) participated in the study. Barthel Index (BI), Cumulative Illness Rating Scale (CIRS) and Mini-BESTest (MBT) were administered to subjects by the same operators. Due to time/location constraints, MBT was only administered to 39 subjects (19 males and 20 females, 76 ± 6 years, 77 ± 12 kg, 168 ± 8 cm). Subjects also performed an instrumented over-ground gait task (on a 100 m long road) wearing an IMU located on the trunk, at the height of the fifth lumbar vertebra. Eleven gait variability/stability measures were calculated on stride time and trunk acceleration data during gait, namely Standard Deviation (SD), Coefficient of Variation (CV), Nonstationary Index (NI), Inconsistency of Variance (IV), Poincaré Plots (PSD1/PSD2), Maximum Floquet Multipliers (maxFM), short/long-term Lyapunov exponents (sLE/lLE), Harmonic Ratio (HR), Index of Harmonicity (IH), Multiscale Entropy (MSE) and Recurrence Quantification Analysis (RQA). Each measure was calculated for anterior–posterior (AP), medio-lateral (ML) and vertical (V) acceleration directions. In order to assess the correlation between clinical parameters and variability/stability measures, log transformed measures were used as inputs for linear regression models. Results: SD, CV, PSD1 and PSD2 showed negative correlation with BI and MBT. The only stability measure that correlated (positively) with MBT and BI was IH in the ML direction. CIRS correlated with MSE (ML and V directions), maxFM and lLE. Discussion and conclusions: BI and MBT negatively correlated with stride time variability measures, meaning that a relationship exists between the deterioration of the overall motor functionality and the increase in stride time variability. BI and MBT were also found to be linked to the harmonicity of acceleration signal in the ML direction, confirming the importance of ML trunk oscillations during gait for functionality assessment. CIRS correlated with stability measures, in particular with MSE in ML and V directions, suggesting a link between cumulative illness and gait stability in elderly subjects. Moreover, MSE was previously found to be linked to fall history in elderly subjects, and should hence to be taken into consideration for gait stability assessment. In conclusion, gait variability and stability measures showed promising correlation with clinical rating scales in the elderly population, and could be considered for complementing the standard clinical scores in the assessment of fall risk. A more reliable quantification of locomotor features could be obtained from instrumental measurements, allowing to avoid inter-operator differences.