Measuring regularity of human postural sway using approximate entropy and sample entropy in patients with Ehlers–Danlos syndrome hypermobility type Chiara Rigoldi a, *, Veronica Cimolin a , Filippo Camerota b , Claudia Celletti b , Giorgio Albertini c , Luca Mainardi a , Manuela Galli a,c a Bioeng. Dept., Politecnico di Milano, Milan, Italy b Physical Medicine and Rehabilitation Division, Umberto I Hospital, Sapienza University, Rome, Italy c IRCCS ‘‘San Raffaele Pisana’’, Tosinvest Sanita `, Rome, Italy 1. Introduction Joint hypermobility syndrome (JHS) is a relatively common, although largely under diagnosed clinical entity, characterized by congenital contortionism and additional musculoskeletal complaints (Steinmann, Royce, & Superti-Furga, 2002). There is a significant clinical overlap with various heritable connective tissue disorders, mainly the Ehlers–Danlos syndrome(s) (EDS) (Grahame, Bird, & Child, 2000). These similarities are so stringent that, recently, an international group of experts stated that JHS and EDS hypermobility type (EDS-HT) are the same clinical entity that should be distinguished from other types of EDS (Tinkle et al., 2009). Major features include joint hypermobility, joint complications and minor skin features (e.g., skin hyperextensibility), while the presence of additional cutaneous, vascular, skeletal and ocular findings moves towards the diagnosis of other EDS variants. Hypotonia in EDS-HT patients can influence the intrinsic information about posture and movement and can have a negative effect on the appropriateness of co-contraction and postural reactions. Increased joint mobility may contribute in a negative sense to postural control: hypermobility may affect the stability based on faulty reflex pattern originating from tendon organs (Røgind, Lykkegaard, Bliddal, & Danneskiold-Samsøe, 2003). Together with Research in Developmental Disabilities 34 (2013) 840–846 A R T I C L E I N F O Article history: Received 12 September 2012 Received in revised form 9 November 2012 Accepted 9 November 2012 Available online 12 December 2012 Keywords: Ehlers–Danlos syndrome Postural analysis Entropy analysis A B S T R A C T Ligament laxity in Ehlers–Danlos syndrome hypermobility type (EDS-HT) patients can influence the intrinsic information about posture and movement and can have a negative effect on the appropriateness of postural reactions. Several measures have been proposed in literature to describe the planar migration of CoP over the base of support, and the most used in clinical field are the CoP excursions in antero-posterior and medio-lateral direction. In recent years a growing number of studies have been designed to explore the complexity of the COP trajectories during quiet standing. We assessed 13 adults with EDS- HT (EDSG) and 20 healthy adults (CG) during static posture, evaluating the CoP using time and frequency domain analysis and entropy analysis (SampEn and ApEn parameters). Higher values of CoP displacements in medio-lateral and anterior–posterior directions for EDSG than CG were found; no differences were observed in CoP frequency. The entropy analysis showed lower value for EDSG than CG, pointing out the needing of EDSG to concentrate more attention on postural control, loosing complexity and reflecting a less automatized postural control. ß 2012 Elsevier Ltd. All rights reserved. * Corresponding author at: Politecnico di Milano, Bioeng. Dept., Via Golgi 39, 20133 Milano, Italy. Tel.: +390223993359, fax: +390223993360. E-mail address: chiara.rigoldi@polimi.it (C. Rigoldi). Contents lists available at SciVerse ScienceDirect Research in Developmental Disabilities 0891-4222/$ – see front matter ß 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ridd.2012.11.007