Biomechanical mechanisms and centre of pressure trajectory during planned gait termination.

AIM: Although gait initiation has been extensively studied, gait termination has received less attention. In particular, the trajectory of the centre of pressure (CoP) during gait termination, as well as the trajectory's determinants, has not yet been described. The purpose of the present study was to characterize the kinetic components of planned gait termination (including the CoP trajectory) with respect to the various gait events and centre of mass speed and trajectory. METHODS: Thirty healthy subjects were asked to walk along a test track and stop on a force platform while an optoelectronic system recorded temporal and spatial parameters. A total of 90 trials were analysed. RESULTS: Subjects needed two steps to stop on the force platform. The CoP trajectory during gait termination was composed of three phases. During the first phase, the CoP moved forward under the stance foot, which was in contact with the ground. The ground reaction forces exerted a sagittal braking action. The second phase showed a lateral CoP shift and was correlated with braking; this may correspond to anticipatory postural adjustments for gait termination. The third and last phase might correspond to compensatory adjustments before the stance phase. CONCLUSIONS: CoP trajectory is more complex during gait termination than during gait initiation. Gait termination comprises several specific sequences in the gait-stance transition. A better understanding of the kinetic parameters in gait termination should enable us to identify which kinetic parameters could be considered as risk factors for falls.

Effect of bilateral subthalamic nucleus deep brain stimulation on postural adjustments during arm movement.

OBJECTIVE: Although it is well known that postural adjustment (PA) is impaired in advanced Parkinson's disease (PD), the potentially compensatory effects of bilateral subthalamic nucleus deep brain stimulation (STN DBS) in this respect are less clear. METHODS: While standing on a force platform and in the absence of antiparkinsonian medication, 10 patients performed voluntary, unilateral arm movements before surgery (the 'off stim' condition) and then afterwards (the 'on stim' condition). The patients' PAs were monitored by vertical torque (Tz) and compared with those recorded in control subjects. RESULTS: Patients with STN DBS and control subjects showed similar values for PA amplitude, duration and latency. CONCLUSIONS: STN stimulation may induce better postural control during the movement preparation and execution phases. Our results argue in favour of a positive effect of STN DBS on PA. SIGNIFICANCE: The PA amplitude (provided by Tz) may be a strong marker reflecting the clinical improvement seen in stimulated PD patients.

Externally provoked freezing of gait in open runways in advanced Parkinson's disease results from motor and mental collapse.

Freezing of gait (FOG) in Parkinson's disease (PD) is defined as a sudden inability to maintain effective stepping movements. However, its pathophysiology remains unclear. The objectives are: (1) To assess the contribution of both spatial (walking speed, stride length) and temporal parameters (cadence, stride time) and their coefficients of variation to the genesis of FOG in PD. (2) To evaluate whether and how externally imposed modifications of self-determined gait would elicit FOG. We included ten patients with advanced PD, and with daily off drug FOG episodes. We focused on walking in an open runway. For each subject, we manipulated gait by externally imposing four changes in walking speed and four changes in cadence. FOG episodes, often with a long duration of more than 5-s, were observed mostly under conditions with a high imposed cadence. The steps that immediately preceded these episodes were mainly characterized by an increase in cadence and an increase in stride length variability. The results also underscore that FOG can be elicited in a laboratory setting when patients are placed under considerable strain, at least in advanced stages of PD. Patients were unable to adequately negotiate the extreme imposed cadence condition, and this resulted in frequent FOG episodes, even while walking in an open runway. Placing advanced PD patients into extreme imposed conditions leads to a motor wise and mental collapse response, culminating in FOG. Future work should establish the relevance of these findings for the more common forms of FOG, including brief episodes during turning or gait initiation.

STN-DBS frequency effects on freezing of gait in advanced Parkinson disease.

BACKGROUND: Severe gait disturbances and freezing episodes (frequently resistant to optimal dopaminergic treatment) often appear in advanced Parkinson disease (PD). Even several years after initiation, high-frequency subthalamic nucleus deep brain stimulation (STN-DBS) is still very effective for controlling segmental symptoms. However, there are no long-term data on the management of gait disorders and freezing in STN-DBS. OBJECTIVES: To compare the effects of various STN-DBS parameters on freezing of gait and to determine whether such effects are more related to stimulation energy (usual voltages vs high voltages at 130 Hz) or frequency (130 Hz vs approximately half this frequency: 60 Hz). METHODS: We blindly assessed STN-DBS parameters in 13 PD patients reporting severe gait disorders. We compared the effects on gait of two different voltages (the patient's usual voltage [median 3 volts] and a high voltage [median 3.7 volts]) and two different frequencies (60 and 130 Hz, while maintaining the same total energy delivered) vs "off-stimulation" conditions. RESULTS: The number of freezing episodes was significantly lower at the 60-Hz "high voltage/equivalent energy" and higher at the 130-Hz/high voltage than for "off stimulation." The slight improvement in the Unified Parkinson's Disease Rating Scale motor score observed (at 130 Hz) did not achieve statistical significance. CONCLUSIONS: Our results prompt consideration of a new strategy for two-stage subthalamic nucleus deep brain stimulation (STN-DBS) frequency optimization, with stimulation at 130 Hz and the usual voltage during the initial years of STN-DBS and then at 60 Hz at a high voltage in Parkinson disease patients who develop severe gait disorders.

[Evolution of locomotion disorders in Huntington's disease]. / Caractéristiques évolutives des troubles de locomotion dans la maladie de Huntington.

INTRODUCTION: Locomotion disorders are important in Huntington's disease (HD). Although the rates of evolution of motor, functional or cognitive aspects of HD have been studied, the evolution of locomotion disorders in early stages of the disease remains unknown. OBJECTIVES: To determine the rate of evolution of the HD-associated gait and gait initiation disorders and their correlates. PATIENTS AND METHODS: Eighteen HD patients were recorded with a minimum interevaluation interval of one year. Akinesia was studied by evaluating the anticipatory postural adjustment (APA) phase preceding the first step. We also evaluated gait speed, stride time and stride length. RESULTS: We observed an alteration in the APA phase, whose evolution was correlated with that of akinesia. We also observed a decrease in gait speed, which was due both to an increase in stride time and a decrease in stride length. Stride-to-stride variability did not worsen between both evaluations. CONCLUSIONS: A worsening in both gait initiation and gait performance was observed in HD. Initial weak functional capacity and more severe motor impairment seem to be associated with a faster progression of locomotion parameters in these mildly impaired HD patients.

Anticipatory postural adjustments associated with arm movement in Parkinson's disease: a biomechanical analysis.

OBJECTIVE: To study anticipatory postural adjustments (APAs) in Parkinson's disease (PD) via a biomechanical analysis, including vertical torque (Tz). METHODS: Ten patients with PD (in the "off-drug" condition) and 10 age matched controls were included. While standing on a force platform, the subject performed a right shoulder flexion in order to grasp a handle in front of him/her, under three conditions (all at maximal velocity): movement triggered by a sound signal and loaded/non-loaded, self-paced movement. The anteroposterior coordinates of the centre of pressure (COP) and Tz were calculated. RESULTS: A group effect was observed for Tz and COP in patients with PD (compared with controls): the maximal velocity peak appeared later and the amplitude of the COP backward displacement and the area of the positive phase of Tz were lower, whereas the duration of the positive phase of Tz was greater. Interaction analysis showed that the area of Tz was especially affected in the triggered condition and the loaded, self-paced condition. The onset of the COP backward displacement was delayed in the triggered condition. CONCLUSION: Our biomechanical analysis revealed that patients with PD do indeed perform APAs prior to unilateral arm movement, although there were some abnormalities. The reduced APA magnitude appears to correspond to a strategy for not endangering postural balance.

A biomechanical study of gait initiation in Huntington's disease.

BACKGROUND: Akinesia in basal ganglia disorders is essentially defined by delayed movement initiation; the reaction time increases and it becomes difficult (or even impossible) for the subject to initiate movement. A biomechanical study of gait initiation would help evaluate the role of akinesia in early stage Huntington's disease (HD) patients. METHODS: We recorded kinematic, spatiotemporal and angular parameters (using video motion analysis, a force platform and an optoelectronic system) for the first two steps taken by 15 HD patients and 15 gender- and age-matched controls. In order to evaluate the influence of an external cue on gait initiation parameters, we studied two movement paradigms: self-triggered initiation and initiation triggered (cued) by a "beep" sound. We analyzed kinematic, spatiotemporal (the speed, length and duration of the two first steps) and angular parameters (range of joint angles) as well as kinetic data (the trajectory of the centre of pressure (COP); the speed and trajectory of the centre of mass (COM)). RESULTS: HD patients presented akinesia in both externally triggered and self-triggered conditions. Patients had more difficulties with self-triggered gait than with triggered gait. In HD, anticipatory postural adjustments (APAs) were more impaired in self-triggered gait initiation than in cued initiation. Indeed, an alteration in the kinetic parameters revealed a reduction in first step speed in both conditions. Hypokinesia (as assessed by a reduction in the range of angle joints) played an important role in this reduction. CONCLUSION: Akinesia is a major feature of impaired gait initiation in HD. The deficiencies in self-triggered initiation in HD seen here fit with a hypothesis whereby deficient internal cueing can be replaced by an external trigger.

Gait abnormalities induced by acquired bilateral pallidal lesions: a motion analysis study.

BACKGROUND: Bilateral pallidal lesions induce a range of cognitive and motor disorders, principally a parkinsonian syndrome in which severe disturbances of gait and gait initiation are frequently reported. However, the precise clinical features of these disorders (and the role of the pallidum therein) remain to be established. OBJECTIVES: The goal of this study was to characterise gait and gait initiation disorders within the context of a parkinsonian syndrome in patients with acquired, bilateral, pallidal lesions (PAL patients), to compare these disorders to those seen in Parkinson's disease (PD), and to assess the corresponding physiopathological implications. PATIENTS AND METHODS: By using a video motion analysis system (VICON), we studied gait kinematic parameters in two patients presenting with bilateral, pallidal lesions. Kinematic and kinetic parameters were also determined during gait initiation. The two patients were compared with a group of 17 PD patients and to 20 healthy controls. RESULTS: In both PAL and PD patients, kinematic parameters (gait and gait initiation) and kinetic parameters (gait initiation) were similarly impaired, evidenced by akinesia (difficulty in initiating gait characterized by impairment of anticipatory postural adjustments). Hypokinesia and bradykinesia (respectively reduced stride length and reduced speed during gait) were also noted. CONCLUSION: The gait and gait initiation disorders seen in cases of bilateral pallidal lesions (namely akinesia, hypokinesia and bradykinesia) are similar to those observed in PD. Subject to confirmation in more extensive studies, we hypothesize that bipallidal patients may present higher level gait disorders,with potential mediation by cognitive impairment.

[Differences in anticipatory postural adjustments between self-generated and triggered gait initiation in 20 healthy subjects]. / Caractérisation des ajustements posturaux lors d'une initiation de la marche déclenchée par un stimulus sonore et autocommandée chez 20 sujets sains.

OBJECTIVE: Preparation of upper-limb movements differs between self-paced and triggered conditions. This study analyzed the anticipatory postural adjustments (APAs) of gait initiation in normal subjects in 2 conditions: self-generated and triggered by a "beep" sound. METHODS: We recorded kinematic, spatiotemporal parameters of the first two steps by means of video motion analysis (6 infrared cameras), and kinetic parameters (using a force platform and the optoelectronic system) in 20 normal subjects. Two conditions: 1) self-generated initiation; and 2) initiation triggered by a "beep" sound were studied to evaluate the APA phase, by recording kinetic data (duration of the APAs, trajectory of the center of pressure, speed and trajectory of the center of mass). Kinematic data (first and second step speed, length and duration) were also recorded. RESULTS: First step speed and length were increased in self-paced gait initiation compared to triggered gait initiation in controls. We found no difference between the 2 conditions in terms of second step kinematic data. It was caused by a significant difference between the 2 conditions for the temporal characteristics of anticipatory postural adjustments (APAs) in the initiation of the first step, which was longer when normal subjects performed self-generated gait initiation. The trajectory of center of pressure and center of mass remained the same in the 2 conditions. CONCLUSION: APAs of gait initiation process are delayed under self-paced condition, although they do not differ qualitatively between reaction time and self-paced condition. Neuphysiological support of self-generated movement could explain these differences.

Chronic bilateral pallidal stimulation and levodopa do not improve gait in the same way in Parkinson's disease: a study using a video motion analysis system.

Chronic bilateral internal globus pallidus (GPi) stimulation allows control of levodopa induced dyskinesias (LID) and motor symptoms in severe Parkinson's disease (PD). The effect on gait has not been clearly established. Different results have been reported, mostly consisting of clinical data. The aim of this study was to evaluate, by means of a video motion analysis system (optoelectronic VICON system), the influence of bilateral GPi stimulation on gait in PD. Five patients underwent bilateral GPi stimulation. The preoperative and postoperative (3 months after surgery) clinical gait disturbances (items 29 and 30 of the motor UPDRS), as well as spatial and temporal gait measurements (namely cadence, velocity, stride and step times, single and double limb support times, stride and step lengths) were analysed in off condition (the patient had received no treatment for 12 hours or merely the lowest dose of levodopa allowing him to walk for the gait analysis) and in the on drug condition (after administration of 200 mg of levodopa). The gait analysis was performed with the VICON system. In off condition, there was a statistically significant improvement after surgery for UPDRS III and gait (clinically assessed). In on drug condition, there was a significant improvement for LID whereas UPDRS III and clinical assessment of gait were unchanged. The VICON system also showed that surgery improved gait especially in off condition, but also in on drug condition. Our method allowed exact quantification of the influence of surgery on gait characteristics. As compared with levodopa treatment, the effect of stimulation seems to be different. Indeed, the results suggest only limited effects of pallidal stimulation on the control of stride length and rather point to compensatory additional mechanisms.

[Tridimensional gait analysis after unilateral subtalar arthrodesis]. / Analyse tridimensionnelle de la marche après arthrodèse sous astragalienne unilatérale.

PURPOSE OF THE STUDY: Subtalar arthrodesis can be useful in various conditions. Initially used for the treatment of congenital or acquired foot deformities, it was later applied to surgical repair of traumatic injury. The subtalar joint does however play an important role in gait, particularly for transmitting rotational movement of the leg to the foot. The functional outcome after subtalar arthrodesis has been the object of many studies. These studies examined clinical and radiological results and raised the problem of determining the appropriate extent of the fusion. None of these studies has however provided a three-dimensional analysis of gait after subtalar arthrodesis, performed in the present work. MATERIAL AND METHODS: We used the Vicon VX3D system with 2 integrated force platforms. Acquisition was made at 50 Hz. The Vicon recording was coupled with EMG recordings of the gastrocnemius, the rectus, the anterior tibialis, and the glutius medius. Gait was analyzed in 8 patients who had undergone unilateral subtalar arthrodesis at least 18 months earlier. Several recordings were made for each patient but only one complete gait cycle was retained for analysis of kinematic, kinetic and electromyographic curves and ground reaction forces. Wilcoxon's test for paired series was used to compare the operated side to the healthy side (excepting EMG recordings). RESULTS: The operated and healthy side were significantly different. Total amplitude of joint movement was lower for the operated side: 16.5 degrees versus 21.5 degrees for the healthy side. Peak power generated at the ankle for plantar flexion was lower at the end of the stance phase. Electromyography recordings showed a shift in muscle activity between the healthy and fused foot. DISCUSSION: Few statistical differences were found between the tested values. It can thus be concluded that gait pattern is globally symmetrical after subtalar arthrodesis and that this fusion has little functional impact on the knee or the hip. The difference in amplitude between the healthy and operated side showed a wider variability than observed by Winter in the healthy subject that was also greater than the measurement error reported by Laasel. We did not perform a statistical analysis of the EMG data since the values recorded were arbitrary and the observed shift in activities had no general impact. CONCLUSION: Despite the reduction in flexion-extension amplitude of the ankle, subtalar arthrodesis allows a globally symmetrical gait in the experimental conditions described.

[A tridimensional study of lateral grasping and pointing in spatial neglect]. / Une analyse tridimensionnelle de la saisie et du pointage latéraux dans la négligence spatiale.

The aim of this study was to analyze the ipsilateral upper limb and head kinematics in patients presenting with spatial neglect, using pointing and grasping to object. Four patients were included and compared to an equivalent number of normal subjects. Head, shoulder, and wrist movements were recorded using a three-dimensional VICON system. Objects to be pointed or grasped were localized in the right or left space facing the subject. Patients presented with a reduction in the mean wrist velocity, which was more obvious when directed to the left side, reduction in the peak velocity, and a severe increase of the time between the peak velocity and the end of the movement. The amplitude and mean velocity of left head movements were comparable in both groups. The analysis of the intersegmental co-ordination showed that the sequence of activation of corporeal segments was similar in patients and controls: head movement, shoulders rotation, upper limb extension. Co-ordination between head and wrist movements was assessed using the cross-correlation method. An increase in time lag and a reduction in crossed correlations between the head and wrist movements was observed in leftward movements of neglect patients, but the co-ordination between the shoulder and wrist movements was preserved. Thus, we demonstrated a global disorder of intentional movements in patients, which was relatively similar in pointing and grasping to object, and predominated on the approach phase, which is associated to important visuo-motor adjustments. This study also demonstrated desynchronization of head and wrist movements, which can be an important problem in neglect patients.

Effect of thalamic stimulation on gait in Parkinson disease.

OBJECTIVE: To assess the influence of ventral intermediate thalamic nucleus stimulation on gait in idiopathic Parkinson disease. DESIGN: Clinical and physiological assessments were compared in patients with and without ventral intermediate thalamic nucleus stimulation. SETTING: The research clinic of a university department of gait analysis. PATIENTS: Seven patients with idiopathic Parkinson disease who had long-term monopolar stimulation of the ventral intermediate thalamic nucleus to control a large-amplitude tremor. MAIN OUTCOME MEASURES: Gait kinematic parameters were autonomically recorded using the Vicon optoelectric system for movement analysis. Measures of locomotor displacement (cadence, walking speed, stride and step times, single and double support times, and stride and step lengths) were computed successfully during 2 conditions: stimulation on and off. Traces of ankle joint position were also analyzed for the left and right lower limbs and for the affected and unaffected lower limbs. RESULTS: No difference in mean values was observed between the 2 conditions. CONCLUSION: This study seems to confirm that ventral intermediate thalamic nucleus stimulation, effective in reducing tremor, does not modify gait parameters in idiopathic Parkinson disease.

[Lambert-Eaton syndrome. Diagnostic, nosologic and therapeutic problems]. / Le syndrome de Lambert-Eaton. Problèmes diagnostiques nosologiques et thérapeutiques.

We report on five cases of this myasthenic disorder associated with a loss of deep tendon reflexes, dry mouth and impotence. The diagnosis relies upon the response to repeated electric stimulations: with stimulations at a frequency of 5 Hz, the size of the potentials decreases by more than 30 p. 100 and, at 30 Hz, increases by more than 60 p. 100. This profile differentiates Lambert-Eaton syndrome from myasthenia gravis. Lambert-Eaton syndrome occurs usually in the course of malignant diseases; when it seems isolated, a visceral neoplasm, mainly bronchogenic carcinoma, should be suspected. Nevertheless, in some cases, no malignant disease is found. The mechanism is a presynaptic block of neuromuscular transmission because of an unknown hypothetic substance produced by the tumor. Therapeutic resources (Guanidine) are scarce.