title: The effect of axis alignment on shoulder joint kinematics analysis during arm abduction.
abstract: BACKGROUND
  A joint coordinate system allows coherence between the performed movement, its mathematical representation and the clinical interpretation of the kinematics of joint motion. In 2005, the International Society of Biomechanics (ISB) defined a joint coordinate system for the shoulder. To improve kinematics interpretation, the ISB suggested aligning the coordinate systems of the humerus and the scapula. Therefore, the aim of this research project was to determine how the alignment of the joint coordinate system axes can influence the interpretation of shoulder joint kinematics. More precisely, we wanted to investigate if mathematical alignment of the reference and moving coordinate system axes could facilitate the kinematic interpretation of a simple abduction movement without introducing additional coupled motion.
  
  
  METHODS
  An experiment was carried out on eight shoulder cadaveric specimens. Elevation of the arm in the scapular plane (abduction) was recorded using an electromagnetic tracking device. Three-dimensional angular displacements of the arm during elevation in the scapular plane were described using the standard ISB joint coordinate system, and using a modified joint coordinate system for which the axes were mathematically aligned.
  
  
  RESULTS
  The results obtained revealed a difference in the interpretation of the starting angles between the ISB joint coordinate system and the aligned coordinate system. No difference was found in the interpretation of the angular range of motion (P<0.01).
  
  
  CONCLUSIONS
  The aligned coordinate system provided a standardized starting angle of elevation that allows an easier clinical interpretation of shoulder kinematics.
authors.affiliation: Laboratoire de recherche en imagerie et orthopédie, Centre de recherche, Centre hospitalier de l'Université de Montréal (CHUM), Montréal, Canada.
authors.forename: Annie
authors.initials: A
authors.lastname: Levasseur
authors.forename: Patrice
authors.initials: P
authors.lastname: Tétreault
authors.forename: Jacques
authors.initials: J
authors.lastname: de Guise
authors.forename: Natalia
authors.initials: N
authors.lastname: Nuño
authors.forename: Nicola
authors.initials: N
authors.lastname: Hagemeister
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001132:Arm / Q000033:anatomy & histology* / Q000502:physiology*; D001696:Biomechanical Phenomena / Q000379:methods; D002102:Cadaver; D003198:Computer Simulation; D006801:Humans; D008875:Middle Aged; D008954:Models, Biological; D009068:Movement / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology*; D012399:Rotation; D012785:Shoulder Joint / Q000033:anatomy & histology* / Q000502:physiology*