Time profile of kinematic synergies of stroke gait.

BACKGROUND: In stroke subjects, the motor skills differ between sides and among subjects with different levels of motor recovery, impacting inter-joint coordination. How these factors can affect the kinematic synergies over time during gait has not been investigated yet. This work aimed to determine the time profile of kinematic synergies of stroke patients throughout the single support phase of gait. METHODS: Kinematic data from 17 stroke and 11 healthy individuals was recorded using a Vicon System. The Uncontrolled Manifold approach was employed to determine the distribution of components of variability and the synergy index. To analyze the time profile of kinematic synergies, we applied the statistical parametric mapping method. Comparisons were made within the stroke group (paretic and non-paretic limbs) and between groups (stroke and healthy). The stroke group was also subdivided into subgroups with worse and better motor recovery. FINDINGS: There are significant differences in synergy index at the end of the single support phase between stroke and healthy subjects; paretic and non-paretic limbs; and paretic limb according to the motor recovery. Comparisons of mean values showed significantly larger values of synergy index for the paretic limb compared to the non-paretic and healthy. INTERPRETATION: Despite the sensory-motor deficits and the atypical kinematic behavior, stroke patients can produce joint covariations to control the center of mass trajectory in the forward progression plane, but the modulation of the synergy is impaired, reflecting altered adjustments, especially in the paretic limb of subjects with worse levels of motor recovery.

Does thenumber of stepsneededfor UCM gait analysisdiffers between healthy and stroke?

The basis for the uncontrolled manifold (UCM) approach is the variability among repetitions of a motor task. Thus, reliable results might be influenced by the number of trials. This study estimated the number of steps needed for UCM analysis of stroke gait and if it is the same for healthy subjects. Twenty-five volunteers participated, sixteen in the stroke group (age 59.0 ± 7.5 years, ten hemiparesis at right), and nine in the healthy group (age 59.2 ± 4.9 years). We applied the UCM analysis over each lower limb's single support phase (SSP). The center of mass in the sagittal plane was the task variable, and the ankle, knee and hip joint angles, the elemental variables. The results obtained with 40 steps were used as a reference and compared with those obtained separately from 10, 20, and 30 steps. The mean values of the curves along the SSP were compared between the sets of steps. Further, for each volunteer, we calculated the Pearson correlation between the 40 steps curve and those obtained with other numbers of steps. Our results indicate that (1) the number of steps necessary to perform UCM analysis of stroke gait is larger than those necessary in healthy condition, (2) the synergy index is less sensitive to the number of steps than the UCM components (V_UCM and V_ORT), and (3) the analysis of the UCM over time requires a more significant number of steps than the mean values.

Center of mass in analysis of dynamic stability during gait following stroke: A systematic review.

BACKGROUND: The Center of mass (CoM) analysis reveals important aspects of gait dynamic stability of stroke patients, but the variety of methods and measures represents a challenge for planning new studies. RESEARCH QUESTION: How have the CoM measures been calculated and employed to investigate gait stability after a stroke? Three issues were addressed: (i) the methodological aspects of the calculation of CoM measures; (ii) the purposes and (iii) the conclusions of the studies on gait stability that employed those measures. METHODS: PubMed and Science Direct databases have been searched to collect original articles produced until July 2017. A set of 26 studies were selected according to criteria involving their methodological quality. RESULTS: A compromise between accuracy and feasibility in CoM calculation could be reached using the segmental method with 7-9 segments. Regarding their purposes, two types of studies were identified: clinical and research oriented. From the first ones, we highlighted: the margin of stability (MoS) in the mediolateral (ML) direction, and the angular momentum in the frontal plane could be indicators of dynamical stability; the MoS in the anteroposterior (AP) direction might be able to detect the risk of falls and the symmetry of vertical CoM displacement could be used to analyze energy expenditure during gait. These and other CoM measures are potentially useful in clinical settings, but their psychometric properties are still to be determined. The research oriented studies allowed to clarify that stability is not improved by widening the step in stroke patients and that the impaired control of the non-paretic limb might be the main source of instability. SIGNIFICANCE: This review provides recommendations on the methods for estimating CoM and its measures, identifies the potential usefulness of CoM parameters and indicates issues that could be addressed in future studies.

Influence of feet position on COP measures in post-stroke patients in quiet standing.

BACKGROUND: Foot placement is an important methodological parameter in experiments for analyzing the behavior of the center of pressure (CoP) duringquiet standing. In the case of stroke patients, this is a relevant issue, as the standardized position, usually adopted is not ecological. RESEACH QUESTION: Do between-limb synchronization, weight-bearing symmetry, and amplitude of the postural sway of post-stroke individuals differ between standardized and comfortable foot positions during quiet standing? METHODS: A total of 36 volunteers (20 with stroke and 16 healthy) stood barefoot, for 60 s, on two force plates with feet in a comfortable and standardized position (14° of external rotation and heels 17 cm apart). Three trials were performed in each position, and the average values obtained were analyzed. RESULTS: The comfortable position adopted by stroke individuals was characterized by heels kept 17 cm apart and with 21° of external rotation. None of the measures of the healthy group were influenced by feet position. In the stroke group, the lag to maximal between-feet correlation in the mediolateral direction (ML ρmax lag) was higher (0.45 s) and the weight-bearing symmetry was better in the comfortable (38%) than in the standardized conditions (0.19 s and 32%, respectively). Neither the other CoP measures nor the intra-subject variability was sensitive to feet position. SIGNIFICANCE: The assumption that standardization leads to reduced variability might not be valid to the post-stroke and healthy individuals age around 55 years. Therefore, adoption of a comfortable condition might be advantageous, once it allows for a more practical and realistic evaluation of postural control.

Reliability and Minimum Detectable Change of the Gait Deviation Index (GDI) in post-stroke patients.

The Gait Deviation Index (GDI) is a summary measure that provides a global picture of gait kinematic data. Since the ability to walk is critical for post-stroke patients, the aim of this study was to determine the reliability and Minimum Detectable Change (MDC) of the GDI in this patient population. Twenty post-stroke patients (11 males, 9 females; mean age, 55.2±9.9years) participated in this study. Patients presented with either right- (n=14) or left-sided (n=6) hemiparesis. Kinematic gait data were collected in two sessions (test and retest) that were 2 to 7days apart. GDI values in the first and second sessions were, respectively, 59.0±8.1 and 60.2±9.4 for the paretic limb and 53.3±8.3 and 53.4±8.3 for the non-paretic limb. The reliability in each session was determined by the intra-class correlation coefficient (ICC) of three strides and, in the test session, their values were 0.91 and 0.97 for the paretic and non-paretic limbs, respectively. Between-session reliability and MDC were determined using the average GDI of three strides from each session. For the paretic limb, between-session ICC, standard error of measurement (SEM), and MDC were 0.84, 3.4 and 9.4, respectively. Non paretic lower limb exhibited between-session ICC, standard error of measurement (SEM), and MDC of 0.89, 2.7 and 7.5, respectively. These MDC values indicate that very large changes in GDI are required to identify gait improvement. Therefore, the clinical usefulness of GDI with stroke patients is questionable.

Reliability and minimum detectable change of the gait profile score for post-stroke patients.

The objectives of this work were (i) to determine Gait Profile Score (GPS) for hemiparetic stroke patients, (ii) to evaluate its reliability within and between sessions, and (iii) to establish its minimal detectable change (MDC). Seventeen hemiparetic patients (mean age 54.9±10.5years; 9 men and 8 women; 6 hemiparetic on the left side and 11 on the right side; mean time after stroke 6.1±3.5months) participated in 2 gait assessment sessions within an interval of 2-7 days. Intra-session reliability was obtained from the intraclass correlation coefficient (ICC) between the three strides of each session. Inter-session reliability was estimated by the ICC from the averages of that three strides. GPS value of non paretic lower limb (NPLL) (13.9±2.4°) was greater than that of paretic lower limb (PLL) (12.0±2.8°) and overall GPS (GPS_O) was 13.7±2.5°. The Gait Variable Scores (GVS), GPS and GPS_O exhibited intra-session ICC values between 0.70 and 0.99, suggesting high intra-day stability. Most of GVS exhibited excellent inter-session reliability (ICC between 0.81 and 0.93). Only hip rotation, hip abduction of PLL exhibited moderate reliability with ICC/MDC values of 0.57/10.0° and 0.71/3.1°, respectively. ICC/MDC values of GPS were 0.92/2.3° and 0.93/1.9° for PLL and NPLL, respectively. GPS_O exhibited excellent test-retest reliability (ICC=0.95) and MDC of 1.7°. Given its reliability, the GPS has proven to be a suitable tool for therapeutic assessment of hemiparetic patients after stroke.