title: A method of measuring three-dimensional scapular attitudes using the optotrak probing system.
abstract: OBJECTIVE
  To develop a method to obtain accurate three-dimensional scapular attitudes and to assess their concurrent validity and reliability.
  
  
  METHODS
  In this methodological study, the three-dimensional scapular attitudes were calculated in degrees, using a rotation matrix (cyclic Cardanic sequence), from spatial coordinates obtained with the probing of three non colinear landmarks first on an anatomical model and second on a healthy subject.
  
  
  BACKGROUND
  Although abnormal movement of the scapula is related to shoulder impingement syndrome, it is not clearly understood whether or not scapular motion impairment is a predisposing factor. Characterization of three-dimensional scapular attitudes in planes and at joint angles for which sub-acromial impingement is more likely to occur is not known.
  
  
  METHODS
  The Optotrak probing system was used. An anatomical model of the scapula was built and allowed us to impose scapular attitudes of known direction and magnitude. A local coordinate reference system was defined with three non colinear anatomical landmarks to assess accuracy and concurrent validity of the probing method with fixed markers. Axial rotation angles were calculated from a rotation matrix using a cyclic Cardanic sequence of rotations. The same three non colinear body landmarks were digitized on one healthy subject and the three dimensional scapular attitudes obtained were compared between sessions in order to assess the reliability.
  
  
  CONCLUSIONS
  The measure of three dimensional scapular attitudes calculated from data using the Optotrak probing system was accurate with means of the differences between imposed and calculated rotation angles ranging from 1.5 degrees to 4.2 degrees. Greatest variations were observed around the third axis of the Cardanic sequence associated with posterior-anterior transverse rotations. The mean difference between the Optotrak probing system method and fixed markers was 1.73 degrees showing a good concurrent validity. Differences between the two methods were generally very low for one and two direction displacements and the largest discrepancies were observed for imposed displacements combining movement about the three axes. The between sessions variation of three dimensional scapular attitudes was less than 10% for most of the arm positions adopted by a healthy subject suggesting a good reliability. The Optotrak probing system used with a standardized protocol lead to accurate, valid and reliable measures of scapular attitudes.
  
  
  CONCLUSIONS
  Although abnormal range of motion of the scapula is often related to shoulder pathologies, reliable outcome measures to quantify three-dimensional scapular motion on subjects are not available. It is important to establish a standardized protocol to characterize three-dimensional scapular motion on subjects using a method for which the accuracy and validity are known. The method used in the present study has provided such a protocol and will now allow to verify to what extent, scapular motion impairment is linked to the development of specific shoulder pathologies.
authors.affiliation: Institut de réadaptation en Déficience Physique de Québec, Groupe de Recherche en Réadaptation Physique de l'Université Laval, 525, boul. Wilfrid-Hamel, bureau B-77, Quebec, Canada. ljhebert@microtec.net
authors.forename: L J
authors.initials: LJ
authors.lastname: Hébert
authors.forename: H
authors.initials: H
authors.lastname: Moffet
authors.forename: B J
authors.initials: BJ
authors.lastname: McFadyen
authors.forename: G
authors.initials: G
authors.lastname: St-Vincent
mesh_terms: D001696:Biomechanical Phenomena; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000295:instrumentation*; D008953:Models, Anatomic; D016059:Range of Motion, Articular / Q000502:physiology; D015203:Reproducibility of Results; D012399:Rotation; D012540:Scapula / Q000033:anatomy & histology* / Q000502:physiology*; D018709:Statistics, Nonparametric