title: Verification of skin-based markers for 3-dimensional kinematic analysis of the equine tarsal joint.
abstract: BACKGROUND
  Kinematic studies are usually based on tracking markers attached to the skin. However, complex joints, such as the tarsal joint, function in 3-dimensions (3D), and have therefore necessitated application of the invasive bone pin technique, limiting kinematic studies to the research laboratory. This study investigates the feasibility of using skin-based markers for 3D analysis of tarsal joint motion.
  
  
  OBJECTIVE
  Three-dimensional motions of the tarsal joint can be measured with an acceptable degree of accuracy using skin markers.
  
  
  METHODS
  Retroreflective markers were attached over the tibial and metatarsal segments. Markers were tracked automatically at trot. Three-dimensional skin correction algorithms were used for correction of skin displacement, and 3D motions derived from the corrected (CSD) and uncorrected (USD) skin displacement were compared with data from a previous study in which those motions were described using bone-fixed markers (BFM) by correlation, root mean square errors (RMS) and shape agreement (SA) of the curves.
  
  
  RESULTS
  The RMS of BFM and CSD were smaller than those of BFM and USD for all motions. The correlation coefficients of BFM and CSD were higher than those of BFM and USD. SA was good or fair for all motions except internal/external rotation and medial/lateral translation.
  
  
  CONCLUSIONS
  With appropriate correction for skin movement relative to skeletal landmarks, skin markers can identify tarsal 3D motions for flexion/extension, abduction/adduction, cranial/caudal translation, and proximal/distal translation, allowing analysis and comparison of information between horses during swing and stance phases.
authors.affiliation: Faculty of Veterinary Medicine, Chiang Mai University, Thailand.
authors.forename: S
authors.initials: S
authors.lastname: Khumsap
authors.forename: J L
authors.initials: JL
authors.lastname: Lanovaz
authors.forename: H M
authors.initials: HM
authors.lastname: Clayton
mesh_terms: D000465:Algorithms; D000818:Animals; D001696:Biomechanical Phenomena; D005552:Forelimb; D005684:Gait / Q000502:physiology*; D006614:Hindlimb; D006736:Horses / Q000502:physiology*; D021621:Imaging, Three-Dimensional / Q000662:veterinary; D009068:Movement / Q000502:physiology; D012879:Skin Physiological Phenomena; D013640:Tarsal Joints / Q000000981:diagnostic imaging / Q000502:physiology*; D014463:Ultrasonography