Measuring trunk orientation with a CMOS camera: feasibility and accuracy.

ABSTRACT

The purpose of this study was to develop and validate a new tool to objectively quantify trunk orientation at the bedside, especially dedicated to the measurement of the lateropulsion in acute and subacute stroke patients. We developed software to analyze 2D movement with a CMOS camera (Logitech Quickcam Pro 4000) and to calculate the orientation of a segment defined by two color markers. First, the accuracy, reproducibility and noise when measuring segment orientations were evaluated with the CMOS camera placed in different positions, and second trunk orientation was measured in static and in dynamic conditions both with a CMOS camera and with a gold standard 3D video system (BTS SMART-e). Results showed that the measurement was accurate (mean error=0.05+/-0.12 degrees), reproducible (S.D. over five measurements=0.005 degrees ) and steady (noise signal=0.02 degrees ). The data obtained with the CMOS camera were highly correlated with those obtained with the 3D video system both in static and in dynamic conditions. However, the CMOS camera must be relatively well centered on the measured segment to avoid error due to image distortion. The parallax error was negligible. In conclusion, this could be an important step in the postural assessment of acute and subacute stroke patients. The CMOS camera, a simple, portable, compact, low-cost, commercially available apparatus is the first tool to objectively quantify lateropulsion at the bedside. This method could also support the development of a rehabilitation program for trunk orientation based on biofeedback using the real-time signal provided by the device.