title: Affordable clinical gait analysis: an assessment of the marker tracking accuracy of a new low-cost optical 3D motion analysis system.
abstract: BACKGROUND
  3D motion analysis represents a method of collecting objective, accurate and repeatable gait data, however the high cost of equipment inhibits its widespread use in routine clinical practice.
  
  
  OBJECTIVE
  To determine the marker tracking accuracy of a new low-cost optical 3D motion analysis system.
  
  
  METHODS
  Comparative between-system study.
  
  
  METHODS
  Clinical motion analysis laboratories.
  
  
  METHODS
  A rigid cluster of four reflective markers was used to compare a low-cost Optitrack 3D motion analysis system against two more expensive systems (Vicon 612 and Vicon MX). Accuracy was measured by comparing the mean vector magnitudes (between each combination of markers) for each system, and reliability was measured through the coefficients of variation (CV). Gaps in the marker trajectories, which are considered undesirable, were also counted.
  
  
  RESULTS
  In terms of accuracy, the largest disagreement between mean vector magnitudes for Optitrack and Vicon MX was 2.2%. The largest disagreement between Vicon 612 and Vicon MX was 2.1%. Regarding reliability, the mean CV was lowest in Vicon MX (0.3%) and similar in the Vicon 612 (2.5%) and Optitrack (2.3%) systems. The number of trajectory gaps for the Vicon MX, Vicon 612 and Optitrack systems were; zero, six and 11 respectively.
  
  
  CONCLUSIONS
  The Optitrack system provides a low-cost 3D motion analysis system that can offer marker tracking accuracy and reliability which is comparable with an older and still widely used system (Vicon 612). Further development work is required before Optitrack can be used for full 3D gait analysis by physiotherapists and other health professionals.
authors.affiliation: Department of Biomedical Engineering, University of Strathclyde, 106 Rottenrow, Glasgow, G4 0NW, UK. Electronic address: bruce.carse@strath.ac.uk.
authors.forename: Bruce
authors.initials: B
authors.lastname: Carse
authors.forename: Barry
authors.initials: B
authors.lastname: Meadows
authors.forename: Roy
authors.initials: R
authors.lastname: Bowers
authors.forename: Philip
authors.initials: P
authors.lastname: Rowe
mesh_terms: D004867:Equipment Design; D005684:Gait; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000295:instrumentation*; D021621:Imaging, Three-Dimensional / Q000295:instrumentation*; D015203:Reproducibility of Results
keywords: 3D motion capture; Gait analysis; Low-cost; Optical motion capture