Sensori-motor adaptation to knee osteoarthritis during stepping-down before and after total knee replacement

BACKGROUND: Stepping-down is preceded by a shift of the center of mass towards the supporting side and forward. The ability to control both balance and lower limb movement was investigated in knee osteoarthritis patients before and after surgery. It was hypothesized that pain rather than knee joint mobility affects the coordination between balance and movement control. METHODS: The experiment was performed with 25 adult individuals. Eleven were osteoarthritic patients with damage restricted to one lower limb (8 right leg and 3 left leg). Subjects were recruited within two weeks before total knee replacement by the same orthopedic surgeon using the same prosthesis and technics of surgery. Osteoarthritic patients were tested before total knee replacement (pre-surgery session) and then, 9 of the 11 patients were tested one year after the surgery when re-educative training was completed (post-surgery session). 14 adult individuals (men: n = 7 and women: n = 7) were tested as the control group. RESULTS: The way in which the center of mass shift forward and toward the supporting side is initiated (timing and amplitude) did not vary within patients before and after surgery. In addition knee joint range of motion of the leading leg remained close to normal before and after surgery. However, the relative timing between both postural and movement phases was modified for the osteoarthritis supporting leg (unusual strategy for stepping-down) before surgery. The "coordinated" control of balance and movement turned to be a "sequential" mode of control; once the body weight transfer has been completed, the movement onset is triggered. This strategy could be aimed at shortening the duration-time supporting on the painful limb. However no such compensatory response was observed. CONCLUSION: The change in the strategy used when supporting on the arthritis and painful limb could result from the action of nociceptors that lead to increased proprioceptor thresholds, thus gating the proprioceptive inputs that may be the critical afferents in controlling the timing of the coordination between balance and movement initiation control

Do Gravity-Related Sensory Information Enable the Enhancement of Cortical Proprioceptive Inputs When Planning a Step in Microgravity?

International audienceWe recently found that the cortical response to proprioceptive stimulation was greater when participants were planning a step than when they stood still, and that this sensory facilitation was suppressed in microgravity. The aim of the present study was to test whether the absence of gravity-related sensory afferents during movement planning in microgravity prevented the proprioceptive cortical processing to be enhanced. We reestablished a reference frame in microgravity by providing and translating a horizontal support on which the participants were standing and verified whether this procedure restored the proprioceptive facilitation. The slight translation of the base of support (lateral direction), which occurred prior to step initiation, stimulated at least cutaneous and vestibular receptors. The sensitivity to proprioceptive stimulation was assessed by measuring the amplitude of the cortical somatosensory-evoked potential (SEP, over the Cz electrode) following the vibration of the leg muscle. The vibration lasted 1 s and the participants were asked to either initiate a step at the vibration offset or to remain still. We found that the early SEP (90–160 ms) was smaller when the platform was translated than when it remained stationary, revealing the existence of an interference phenomenon (i.e., when proprioceptive stimulation is preceded by the stimulation of different sensory modalities evoked by the platform translation). By contrast, the late SEP (550 ms post proprioceptive stimulation onset) was greater when the translation preceded the vibration compared to a condition without pre-stimulation (i.e., no translation). This suggests that restoring a body reference system which is impaired in microgravity allowed a greater proprioceptive cortical processing. Importantly, however, the late SEP was similarly increased when participants either produced a step or remained still. We propose that the absence of step-induced facilitation of proprioceptive cortical processing results from a decreased weight of proprioception in the absence of balance constraints in microgravity

Vestibular signal processing in a subject with somatosensory deafferentation: The case of sitting posture

<p>Abstract</p> <p>Background</p> <p>The vestibular system of the inner ear provides information about head translation/rotation in space and about the orientation of the head with respect to the gravitoinertial vector. It also largely contributes to the control of posture through vestibulospinal pathways. Testing an individual severely deprived of somatosensory information below the nose, we investigated if equilibrium can be maintained while seated on the sole basis of this information.</p> <p>Results</p> <p>Although she was unstable, the deafferented subject (DS) was able to remain seated with the eyes closed in the absence of feet, arm and back supports. However, with the head unconsciously rotated towards the left or right shoulder, the DS's instability markedly increased. Small electrical stimulations of the vestibular apparatus produced large body tilts in the DS contrary to control subjects who did not show clear postural responses to the stimulations.</p> <p>Conclusion</p> <p>The results of the present experiment show that in the lack of vision and somatosensory information, vestibular signal processing allows the maintenance of an active sitting posture (i.e. without back or side rests). When head orientation changes with respect to the trunk, in the absence of vision, the lack of cervical information prevents the transformation of the head-centered vestibular information into a trunk-centered frame of reference of body motion. For the normal subjects, this latter frame of reference enables proper postural adjustments through vestibular signal processing, irrespectively of the orientation of the head with respect to the trunk.</p

Neuromechanical response of the upper body to unexpected perturbations during gait initiation in young and older adults

Background: Control of upper body motion deteriorates with ageing leading to impaired ability to preserve balance during gait, but little is known on the contribution of the upper body to preserve balance in response to unexpected perturbations during locomotor transitions, such as gait initiation. Aim: To investigate differences between young and older adults in the ability to modify the trunk kinematics and muscle activity following unexpected waist lateral perturbations during gait initiation. Methods: Ten young (25 ± 2 years) and ten older adults (73 ± 5 years) initiated locomotion from stance while a lateral pull was randomly applied to the pelvis. Two force plates were used to define the feet centre-of-pressure displacement. Angular displacement of the trunk in the frontal plane was obtained through motion analysis. Surface electromyography of cervical and thoracic erector spinae muscles was recorded bilaterally. Results: A lower trunk lateral bending towards the stance leg side in the preparatory phase of gait initiation was observed in older participants following perturbation. Right thoracic muscle activity was increased in response to the perturbation during the initial phase of gait initiation in young (+ 68%) but not in older participants (+ 7%). Conclusions: The age-related reduction in trunk movement could indicate a more rigid behaviour of the upper body employed by older compared to young individuals in response to unexpected perturbations preceding the initiation of stepping. Older adults’ delayed activation of thoracic muscles could suggest impaired reactive mechanisms that may potentially lead to a fall in the early stages of the gait initiation

IS THE FEEDFORWARD CONTROL OF HEAD-TRUNK AXIS VERTICALICALITY, IN DANCERS; VISION-DEPENDENT ?

During unilateral leg movements performed while standing, it is necessary to displace the center of gravity towards the other leg in order to maintain equilibrium. In addition, the orientation of particular segments, such as head and trunk, which are used as reference values for organizing the motor act, needs to be preserved. The coordination between equilibrium control and the ability to maintain the orientation of given segments (head, trunk) was previously studied in standing subjects instructed to raise one leg lateral to an angle of 45" in response to a light. Two sources of light placed at eye level indicated the side on which the movement was to be performed. Two control strategies were identified (Mouchnino et al.. 1992). An 'inclination" strategy was used by the naive subjects (n=S). This consisted of an external rotation of the body around the antero-posterior ankle joint axis; a counter-rotation of the head with respect to the trunk was observed, which ensured the stabilization in the horizontal plane of the interorbital line. A 'translation" strategy was used by the dancers (n=5! Here the external rotation of the leg around the ankle joint was associated to a feedforward counter-rotation of the trunk around the coxofemoral joint so that the horizontality of the interorbital line and the verticality of the trunk axis were maintained. This new coordination resulted from long term training and indicates that a new motor program has been elaborated. The present investigation was aimed at exploring the role of vision in the feedforward counter-rotation performed at the hl joint in dancers. Three visual no visual information (blurred vision). conditions were compared: eyes open, eyes closed an 'f' translucent goggles which provide It was shown that in dancers the counter-rotation at the hip joint and the external rotation of the ankle joint occur simultaneously under both conditions of perturbed vision as it was under normal condition (eyes open: 415ms +/-59). The counterrotation of the trunk preceded the inclination of the le towards the supporting side by 7.3ms (+/-46) with eyes closed and by -28ms (+/-119) with translucent goggles. The ankle rotation and the hip counter-rotation were hig hly correlated (r=0.95junder both perturbed conditions of vision (eyes closed and translucent go les) whereas in normal condition the correlation coefficient was lower (r=057). In addition, the maintenance of the shoulder line in the horizontal plane was also reserved as it was in condition eyes open (2' +/-1.2) with both eyes closed (1.5 +/-1.2 ) and translucent goggles (1.8" +/- 1.5). These results indicate that the maintenance of the vertical orientation of the head-trunk axis in dancers was not dependent on vision; other sensors such as otolith graviceptors in the head or possibly muscle proprioceptors of the trunk might be used to maintain the axis of the head-trunk vertical. Mouchnino L Aurenty R., Massion J., PedoMi A (1992) Coordination between equilibrium and head-trunk orientation during leg movement: a new strategy built up by training. J. Neurophysiol., in press