title: Biomechanical analysis of posture in patients with spinal kyphosis due to ankylosing spondylitis: a pilot study.
abstract: OBJECTIVE
  Patients with ankylosing spondylitis may experience a progressive spinal kyphosis, which induces a forward and downward displacement of the centre of mass (COM) of the trunk. In this pilot study, the possible mechanisms used to compensate for the displacement of the trunk COM were analysed.
  
  
  METHODS
  Joint angles of hip, knee and ankle were determined in four patients with ankylosing spondylitis and compared to data of 18 healthy subjects. Each patient stood on a force platform and had to adopt several predefined postures, which were recorded by a video camera.
  
  
  RESULTS
  In three patients, the hips were flexed when standing relaxed, and in all patients hip extension was limited. The knee angles of three patients were smaller and in two patients the angle of the ankles was larger compared to healthy subjects.
  
  
  CONCLUSIONS
  The results suggest that the hip joints are at least no longer involved in balance control. This may imply that conservative therapy should focus on the prevention of restriction of the hip joints.
authors.affiliation: Faculty of Human Movement Sciences, Free University of Amsterdam, The Netherlands.
authors.forename: S D
authors.initials: SD
authors.lastname: Bot
authors.forename: M
authors.initials: M
authors.lastname: Caspers
authors.forename: B J
authors.initials: BJ
authors.lastname: Van Royen
authors.forename: H M
authors.initials: HM
authors.lastname: Toussaint
authors.forename: I
authors.initials: I
authors.lastname: Kingma
mesh_terms: D000328:Adult; D000368:Aged; D000843:Ankle Joint / Q000503:physiopathology; D001696:Biomechanical Phenomena; D006621:Hip Joint / Q000503:physiopathology; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology; D007738:Kyphosis / Q000209:etiology* / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D010865:Pilot Projects; D004856:Postural Balance; D011187:Posture; D013131:Spine / Q000503:physiopathology; D013167:Spondylitis, Ankylosing / Q000150:complications* / Q000503:physiopathology*