title: Biomechanical assessment of balance and posture in subjects with ankylosing spondylitis.
abstract: BACKGROUND
  Ankylosing spondylitis is a major chronic rheumatic disease that predominantly affects axial joints, determining a rigid spine from the occiput to the sacrum. The dorsal hyperkyphosis may induce the patients to stand in a stooped position with consequent restriction in patients' daily living activities. The aim of this study was to develop a method for quantitatively and objectively assessing both balance and posture and their mutual relationship in ankylosing spondylitis subjects.
  
  
  METHODS
  The data of 12 healthy and 12 ankylosing spondylitis subjects (treated with anti-TNF-α stabilized), with a mean age of 51.42 and 49.42 years; mean BMI of 23.08 and 25.44 kg/m(2) were collected. Subjects underwent a morphological examination of the spinal mobility by means of a pocket compass needle goniometer, together with an evaluation of both spinal and hip mobility (Bath Ankylosing Spondylitis Metrology Index), and disease activity (Bath Ankylosing Spondylitis Disease Activity Index). Quantitative evaluation of kinematics and balance were performed through a six cameras stereophotogrammetric system and a force plate. Kinematic models together with a test for evaluating balance in different eye level conditions were developed. Head protrusion, trunk flexion-extension, pelvic tilt, hip-knee-ankle flexion-extension were evaluated during Romberg Test, together with centre of pressure parameters.
  
  
  RESULTS
  Each subject was able to accomplish the required task. Subjects' were comparable for demographic parameters. A significant increment was observed in ankylosing spondylitis subjects for knee joint angle with the target placed at each eye level on both sides (p < 0.042). When considering the pelvic tilt angle a statistically significant reduction was found with the target placed respectively at 10° (p = 0.034) and at 30° (p = 0.019) less than eye level. Furthermore in ankylosing spondylitis subjects both hip (p = 0.048) and ankle (p = 0.029) joints angles differs significantly. When considering the posturographic parameters significant differences were observed for ellipse, center of pressure path and mean velocity (p < 0.04). Goniometric evaluation revealed significant increment of thoracic kyphosis reduction of cervical and lumbar range of motion compared to healthy subjects.
  
  
  CONCLUSIONS
  Our findings confirm the need to investigate both balance and posture in ankylosing spondylitis subjects. This methodology could help clinicians to plan rehabilitation treatments.
authors.affiliation: Department of Information Engineering, University of Padova, Padova, Italy.
authors.forename: Zimi
authors.initials: Z
authors.lastname: Sawacha
authors.forename: Elena
authors.initials: E
authors.lastname: Carraro
authors.forename: Silvia
authors.initials: S
authors.lastname: Del Din
authors.forename: Annamaria
authors.initials: A
authors.lastname: Guiotto
authors.forename: Lara
authors.initials: L
authors.lastname: Bonaldo
authors.forename: Leonardo
authors.initials: L
authors.lastname: Punzi
authors.forename: Claudio
authors.initials: C
authors.lastname: Cobelli
authors.forename: Stefano
authors.initials: S
authors.lastname: Masiero
mesh_terms: D000842:Ankle / Q000502:physiology; D001696:Biomechanical Phenomena; D005260:Female; D019416:Head Movements / Q000502:physiology; D006615:Hip / Q000502:physiology; D006801:Humans; D007717:Knee / Q000502:physiology; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D010388:Pelvis / Q000502:physiology; D004856:Postural Balance / Q000502:physiology*; D011187:Posture / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology; D013131:Spine / Q000502:physiology / Q000503:physiopathology; D013167:Spondylitis, Ankylosing / Q000175:diagnosis / Q000503:physiopathology*