Impact of somatosensory impairment on perceptive mechanisms and postural control, a new model : Ehlers-Danlos syndrome hypermobility type ; Impact d'une déficience somesthésique sur les mécanismes de régulation du contrôle postural : un nouveau modèle, le syndrome d'Ehlers-Danlos de type hypermobile

Ehlers-Danlos syndrome (EDS) is the clinical manifestation of hereditary connective tissue disorders, comprising several clinical forms. The EDS hypermobility type (EDSh) is characterized by generalized joint hypermobility and variable skin hyperextensibility, which both generate somatosensory impairment. Somatosensory system is, together with visual and vestibular systems, crucially involved in sensorimotor system functioning. The aim of this work was to understand the impact of impaired proprioception on perceptive and sensorimotor mechanisms underlying postural control in EDSh patients. Evaluation of postural control was structured around two approaches. The first one was indirect, and evaluated the sensory mechanism underlying vertical perception. The second one was direct, and used detailed stabilometric analyses to investigate postural control.The first objective of this work was to evaluate how somatosensory impairment affects the contribution of spatial frame of reference (allocentric, egocentric, and geocentric) to visual vertical perception. Two types of tests were conducted to assess the vertical perception with and without visual information (Rod and Frame Test, RFT; Subjective visual vertical, SVV). These two studies showed that somatosensory impairment reduces the contribution of egocentric frame of reference (body axis) to vertical perception. In response, patients increase their visual field dependence, and thus, use preferentially allocentric frame of reference. The second axis aimed to identify sensory strategies adopted by these patients and their repercussion on postural regulation mechanisms. To investigate this question, a thorough postural assessment was conducted, using sensory perturbation and dual-task paradigm, and linear and non-linear analyses. We observed that somatosensory impairment impacts muscular proprioceptive contribution to automatic regulation mechanism involved in postural control. These modifications in postural regulation induce an increase of active monitoring of ...