A. Yelnik

Sensory reweighting in controls and stroke patients

OBJECTIVE To test sensitivity to proprioceptive, vestibular and visual stimulations of stroke patients with regard to balance. METHOD The postural control of 20 hemiparetic patients after a single hemispheric stroke that had occurred at least 6 months before the study along with 20 controls was probed with vibration, optokinetic, and vestibular galvanic stimulations. Balance was assessed using a force platform (PF) with two miniature inertial sensors placed on the head (C1) and the trunk (C2) under each sensory condition and measured by three composite scores as the mean displacement of the body (PF, C1, C2) during the stimulation. A subject with a composite score greater than the 75th percentile of the composite scores found in the control subjects was arbitrarily considered to be sensitive to that stimulation. RESULTS Both control and stroke patients showed large inter-individual variations in response to the three types of sensory stimulation. Among the hemiparetic patients, nearly 65% were sensitive to the optokinetic stimulation, 60% to the galvanic stimulation and 65% to the vibration stimulation. In contrast to the control group, all the hemiparetic subjects were sensitive to at least one type of stimulation. CONCLUSION Stroke patients are highly dependent on visual, proprioceptive and vestibular information in order to control their standing posture and individually differ in their relative sensitivity to each type of sensory stimulation. SIGNIFICANCE Contrarily to what one might suppose, the increased visual dependence manifested by stroke patients does not necessarily entail any neglect of proprioceptive and vestibular information.

Motor strategies of postural control after hemispheric stroke

After stroke, the causes of balance disorders include motor disorders, sensory loss, perceptual deficits and altered spatial cognition. This review focuses on motor strategies for postural control after stroke. Weight-bearing asymmetry, smaller surface of stability, increased sway, body tilting and sometimes pushing syndrome are observed. Weakness and sensory impairments account only for some of these disturbances; altered postural reactions and anticipated postural adjustments as well as abnormal synergistic muscular activation play an important part. These disorders are often linked to cognitive impairments (visuospatial analysis, perception of verticality, use of sensory information, attention, etc.), which explain the preeminent disorders of postural control seen with right rather than left-hemisphere lesions. Most of the motor changes are due to an impaired central nervous system but some could be considered adaptive behaviors. These changes have consequences for rehabilitation and need further studies for building customized programs based on the motor comportment of a given patient.

Observational Study of 180° Turning Strategies Using Inertial Measurement Units and Fall Risk in Poststroke Hemiparetic Patients

Objective We analyzed spontaneous 180° turning strategies in poststroke hemiparetic patients by using inertial measurement units (IMUs) and the association of turning strategies with risk of falls. Methods We included right paretic (RP) and left paretic (LP) post-stroke patients, and healthy controls (HCs) from a physical and rehabilitation department in France between July 2015 and October 2015. All subjects were right-handed and right-footed for mobilization tasks. Participants were instructed to turn 180° in a self-selected direction after a 10-m walk while wearing three IMUs on their trunk and both feet. We defined three turning patterns based on the number of external steps (pattern I = 1; II = 2–4 steps; and III ≥ 5) and four turning strategies based on the side chosen to turn (healthy or paretic) and the stance limb used during the first step of the turn (healthy or paretic). Falls in the 6 months after measurement were investigated. Results We included 17 RP [mean (SD) age 57.5 (9.5) years (range 43–73)], 20 LP patients [mean age 60.7 (8.8) years (range 43–63)], and 15 HCs [mean age 56.7 (16.1) years (range 36–83)]. The LP and RP groups behaved similarly in turning patterns, but 90% of LP patients turned spontaneously to the paretic side versus 59% of RP patients. This difference increased with turning strategies: 85% of LP versus 29% of RP patients used strategy 4 (paretic turn side with paretic limb). Patients using strategy 4 had the highest rate of falls. Conclusion We propose to consider spontaneous turning strategies as new indicators to evaluate the risk of fall after stroke. IMU could be routinely used to identify this risk and guide balance rehabilitation programs.

An Automated Recording Method in Clinical Consultation to Rate the Limp in Lower Limb Osteoarthritis.

For diagnosis and follow up, it is important to be able to quantify limp in an objective, and precise way adapted to daily clinical consultation. The purpose of this exploratory study was to determine if an inertial sensor-based method could provide simple features that correlate with the severity of lower limb osteoarthritis evaluated by the WOMAC index without the use of step detection in the signal processing. Forty-eight patients with lower limb osteoarthritis formed two severity groups separated by the median of the WOMAC index (G1, G2). Twelve asymptomatic age-matched control subjects formed the control group (G0). Subjects were asked to walk straight 10 meters forward and 10 meters back at self-selected walking speeds with inertial measurement units (IMU) (3-D accelerometers, 3-D gyroscopes and 3-D magnetometers) attached on the head, the lower back (L3-L4) and both feet. Sixty parameters corresponding to the mean and the root mean square (RMS) of the recorded signals on the various sensors (head, lower back and feet), in the various axes, in the various frames were computed. Parameters were defined as discriminating when they showed statistical differences between the three groups. In total, four parameters were found discriminating: mean and RMS of the norm of the acceleration in the horizontal plane for contralateral and ipsilateral foot in the doctor’s office frame. No discriminating parameter was found on the head or the lower back. No discriminating parameter was found in the sensor linked frames. This study showed that two IMUs placed on both feet and a step detection free signal processing method could be an objective and quantitative complement to the clinical examination of the physician in everyday practice. Our method provides new automatically computed parameters that could be used for the comprehension of lower limb osteoarthritis. It may not only be used in medical consultation to score patients but also to monitor the evolution of their clinical syndrome during and after rehabilitation. Finally, it paves the way for the quantification of gait in other fields such as neurology and for monitoring the gait at a patient’s home.

Quantify osteoarthritis gait at the doctor’s office: a simple pelvis accelerometer based method independent from footwear and aging

The gold standard to evaluate the severity of osteoarthritis in the doctor’s office remains clinical scores (Bellamy 2002). The Western Ontario and McMaster Universities (WOMAC) osteoarthritis inde...

On the importance of local dynamics in statokinesigram: A multivariate approach for postural control evaluation in elderly

The fact that almost one third of population >65 years-old has at least one fall per year, makes the risk-of-fall assessment through easy-to-use measurements an important issue in current clinical practice. A common way to evaluate posture is through the recording of the center-of-pressure (CoP) displacement (statokinesigram) with force platforms. Most of the previous studies, assuming homogeneous statokinesigrams in quiet standing, used global parameters in order to characterize the statokinesigrams. However the latter analysis provides little information about local characteristics of statokinesigrams. In this study, we propose a multidimensional scoring approach which locally characterizes statokinesigrams on small time-periods, or blocks, while highlighting those which are more indicative to the general individual’s class (faller/non-faller). Moreover, this information can be used to provide a global score in order to evaluate the postural control and classify fallers/non-fallers. We evaluate our approach using the statokinesigram of 126 community-dwelling elderly (78.5 ± 7.7 years). Participants were recorded with eyes open and eyes closed (25 seconds each acquisition) and information about previous falls was collected. The performance of our findings are assessed using the receiver operating characteristics (ROC) analysis and the area under the curve (AUC). The results show that global scores provided by splitting statokinesigrams in smaller blocks and analyzing them locally, classify fallers/non-fallers more effectively (AUC = 0.77 ± 0.09 instead of AUC = 0.63 ± 0.12 for global analysis when splitting is not used). These promising results indicate that such methodology might provide supplementary information about the risk of fall of an individual and be of major usefulness in assessment of balance-related diseases such as Parkinson’s disease.