Reliability of Stereo Vision and Vicon Motion Capture Systems for Measurement of Interfragmentary Movements

Abstract

Interfragmentary movement (IFM) of bone fragments in an external fixator is essential for successful fracture healing. A thorough validation of results at the precision level required for accurate IFM measurement has not been extensively conducted in past studies. This paper aims to demonstrate through experimental and theoretical investigations that camera-based systems can be used to measure six degrees of freedom micromovements with sufficient accuracy. A pilot study using a micrometre stage evaluated the ability of Vicon, Alvium, and Canon cameras to measure displacements in 0.05 mm increments. Additionally, the effects of marker size, displacement direction, and camera-to-marker distance on measurement accuracy were examined. The rotational capability of the optical systems was also assessed using the law of propagation of uncertainty for uncorrelated quantities and validated through Monte Carlo simulations. For Vicon cameras, the close camera setup yielded more precise measurements than the standard configuration, with maximum marker error values of 19.1±11.3 μm and 18.7±37.0 μm, respectively. For the same marker size (14 mm diameter) and displacement direction (lateral), Alvium cameras demonstrated improved precision compared to Canon cameras, with maximum marker error values of 8.7±4.4 μm and 20.7±4.8 μm, respectively. Furthermore, the rotational uncertainty was lower for Alvium cameras across all Euler angles than for the other systems tested. These findings lay the groundwork for future studies on IFM measurement and demonstrate that Alvium cameras, when carefully calibrated, can provide accurate IFM measurements in clinical settings.