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

Validity of an android device for assessing mobility in people with chronic stroke and hemiparesis: a cross-sectional study

BACKGROUND

Incorporating instrument measurements into clinical assessments can improve the accuracy of results when assessing mobility related to activities of daily living. This can assist clinicians in making evidence-based decisions. In this context, kinematic measures are considered essential for the assessment of sensorimotor recovery after stroke. The aim of this study was to assess the validity of using an Android device to evaluate kinematic data during the performance of a standardized mobility test in people with chronic stroke and hemiparesis.

METHODS

This is a cross-sectional study including 36 individuals with chronic stroke and hemiparesis and 33 age-matched healthy subjects. A simple smartphone attached to the lumbar spine with an elastic band was used to measure participants' kinematics during a standardized mobility test by using the inertial sensor embedded in it. This test includes postural control, walking, turning and sitting down, and standing up. Differences between stroke and non-stroke participants in the kinematic parameters obtained after data sensor processing were studied, as well as in the total execution and reaction times. Also, the relationship between the kinematic parameters and the community ambulation ability, degree of disability and functional mobility of individuals with stroke was studied.

RESULTS

Compared to controls, participants with chronic stroke showed a larger medial-lateral displacement (p = 0.022) in bipedal stance, a higher medial-lateral range (p < 0.001) and a lower cranio-caudal range (p = 0.024) when walking, and lower turn-to-sit power (p = 0.001), turn-to-sit jerk (p = 0.026) and sit-to-stand jerk (p = 0.001) when assessing turn-to-sit-to-stand. Medial-lateral range and total execution time significantly correlated with all the clinical tests (p < 0.005), and resulted significantly different between independent and limited community ambulation patients (p = 0.042 and p = 0.006, respectively) as well as stroke participants with significant disability or slight/moderate disability (p = 0.024 and p = 0.041, respectively).

CONCLUSION

This study reports a valid, single, quick and easy-to-use test for assessing kinematic parameters in chronic stroke survivors by using a standardized mobility test with a smartphone. This measurement could provide valid clinical information on reaction time and kinematic parameters of postural control and gait, which can help in planning better intervention approaches.

Postural Responses to Achilles Tendon Vibration Depend on Feet Positioning

Mechanical vibration of the Achilles tendon is widely used to analyze the role of proprioception in postural control. The response to this tendon vibration (TV) has been analyzed in the upright posture, but the feet positions have varied in past research. Moreover, investigators have addressed only temporal parameters of the center of pressure (CoP). We investigated the effect of TV on both temporal and spectral characteristics of the CoP motion. Eighteen healthy young adults, stood barefoot, with one foot on each side of a dual platform, wearing glasses with opaque lenses. We applied 20 seconds of Achilles TV (bilaterally with inertial vibrators at a frequency of 80 Hz and an amplitude of .2-.5 mm). We analyzed CoP signals pre-vibration (PRE,4-seconds), during vibration (VIB,20 seconds), and after vibration cessation (REC,20 seconds). We repeated this protocol in natural and standardized positions (15° feet angular opening). For determining CoP amplitude and velocity, we divided the 20 seconds into five phases of four seconds each and calculated spectral parameters for the whole 20-second signals. There was an adaptation process in the speed of the CoP mediolateral (p < .01) and anteroposterior (p < .01) and in the displacement of the CoP anteroposterior (p < .01), with higher values in the VIB condition. Velocity and displacement decreased progressively in the REC condition. Median and peak frequencies were higher in the VIB condition when compared to the REC condition, but only in the mediolateral direction (p = .01). The standardized foot position led to increased speed in CoP mediolateral, anteroposterior, and mediolateral displacement (p < .01). CoP spectral characteristics were not affected by foot positioning. We concluded that adaptation of CoP motion in the presence of TV and after its cessation are observable both in time and frequency domains. Feet positioning influenced CoP motion in the presence of TV and after its cessation but it did not affect its spectral characteristics.

Evaluation of the hoof centre-of-pressure path in horses affected by chronic osteoarthritic pain

INTRODUCTION

The Centre of Pressure (COP) is the single point summarising all forces transferred to the hoof during the stance phase of a stride. COP path (COPp) is the trajectory that COP follows from footstrike to lift-off. Aim of the present study was to characterize the COP and COPp in horses affected by osteoarthritis and chronic lameness.

MATERIALS AND METHODS

Seventeen adult horses with a diagnosis of osteoarthritis and single limb chronic lameness were recruited. The COP was recorded using a wireless pressure measuring system (TekScan®) with sensors taped to the hooves (either fore- or hind limb, depending on lameness location). The COPp coordinates were further processed. Procrustes analysis was performed to assess the variability of single strides COPp and average COPp among strides, gaits, and limbs by calculating Procrustes distances (D-values). A linear mixed-effects model was run to analyse D-values differences for lame and sound limbs. Additionally, average COPp D-values and COPp hoofprint shape indices were compared for lame and sound limbs with the Signed Rank Test.

RESULTS

At walk and trot the single-stride COPp D-values were significantly lower in lame than in sound limbs (marginal effects p<0.001). Analysis of the average COPp D-values confirmed that each hoof COPp is highly consistent with itself over subsequent trials but is different from the contralateral. COPp and hoofprint shape indices did not differ between sound and lame limbs. Footstrike and lift-off within the hoofprint showed that most horses had lateral footstrike and lift-off, independently of the lameness location.

CONCLUSION

Our findings are in line with previous observations that COPp are highly repetitive and characteristic for each horse and limb. There seems to be a further decrease in COPp variability in the presence of a painful limb pathology.

Automatic characterization of stroke patients' posturography based on probability density analysis

OBJECTIVE

The probability density analysis was applied to automatically characterize the center of pressure (COP) data for evaluation of the stroke patients' balance ability.

METHODS

The real-time COP coordinates of 38 stroke patients with eyes open and closed during quiet standing were obtained, respectively, from a precision force platform. The COP data were analyzed and characterized by the commonly used parameters: total sway length (SL), sway radius (SR), envelope sway area (EA), and the probability density analysis based parameters: projection area (PA), skewness (SK) and kurtosis (KT), and their statistical correlations were analyzed. The differences of both conventional parameters and probability density parameters under the conditions of eyes open (EO) and eyes closed (EC) were compared.

RESULTS

The PA from probability density analysis is strongly correlated with SL and SR. Both the traditional parameters and probability density parameters in the EC state are significantly different from those in the EO state. The obtained various statokinesigrams were calculated and categorized into typical sway types through probability density function for clinical evaluation of the balance ability of stroke patients.

CONCLUSIONS

The probability density analysis of COP data can be used to characterize the posturography for evaluation of the balance ability of stroke patients.

Impairments and Compensations of Static Balance and Plantar Load Distribution in Patients With Chronic Stroke: An Observational Study

OBJECTIVES

The purpose of this study was to explore impairment and compensation characteristics of static balance and plantar load distribution in patients with chronic stroke.

METHODS

We recruited 68 patients who had chronic stroke who could stand independently (stroke group) and 30 healthy individuals (control group) with the Zebris FDM platform. Static balance parameters, including center of pressure (COP) ellipse sway area, COP path length, and angle-θ between y and major axis, were compared between 2 groups under standard standing posture. In the stroke group, balance parameters were re-tested under their preferring standing posture. Plantar load distribution was also assessed. Another 8 patients with chronic stroke who could not stand independently and had to rely on a crutch were enrolled to analyze the characteristics of balance compensation.

RESULTS

In the stroke group, the ellipse sway area, COP path length, and angle-θ were significantly larger than those of the control group. Sixty-one (89.7%) patients preferred standing with the affected foot outward-forward supporting, and their preferring standing balance was better than that of standard standing. All patients who could not stand independently tended to compensate for balance with a crutch supporting laterally and also preferred standing with a typical posture- the affected foot was outward-forward.

CONCLUSIONS

In patients post stroke, static balance is impaired mainly at the lateral direction, and patients commonly locate the crutch laterally for compensation of lateral balance. Patients preferred standing with the affected foot outward-forward supporting, and their preferring standing balance was better than that of standard standing, which challenged the necessity of training standing symmetrically.

Impairment characteristics of static balance and plantar load distribution of patients undergoing tibial cortex transverse distraction for diabetic foot ulcers

Objective

Tibial cortex transverse distraction (TCTD) has been recently reported for the treatment of diabetic foot ulcers. Herein, we explored the characteristics of the impairments in static balance and plantar load distribution in patients.

Methods

We performed a retrospective study of 21 patients with diabetic foot ulcers who underwent TCTD, who were regularly followed up for > 1 year after surgery, and 20 healthy individuals (control group). A pressure platform was used to assess the standing balance functions of the lower extremities and the plantar load distribution.

Results

One patient underwent amputation because of severe infection. In patient group, center of pressure (COP) ellipse sway area, COP path length and angle θ were all larger, compared with those of control group (250.15 ± 98.36 mm² vs. 135.67 ± 53.21 mm², 145.15 ± 67.43 mm vs. 78.47 ± 34.15 mm, 39.75 ± 17.61° vs. 22.17 ± 14.15°), with statistically significant differences (P < 0.01). The average plantar load and backfoot load of the unaffected side was significantly larger than that of the affected side (58.4 ± 5.5% vs. 41.6 ± 5.5%, 45.3 ± 6.4% vs. 36.5 ± 5.6%), but they were similar for the two feet of members of the control group.

Conclusions

Although TCTD may represent an appropriate method for the treatment of diabetic foot ulcers, postoperative impairments in static balance and plantar load distribution remain in the long term. These potential long-term problems should be taken into account in further rehabilitation planning.

Type of study/level of evidence: Therapeutic III.