Measurement of scapular kinematics with the moiré fringe projection technique

The aim of this study was to investigate the applicability of the moiré fringe projection technique (MFPT) to quantify the scapular motions relative to the thorax. This system was composed of a LCD projector, a digital photographic camera, and a microcomputer. To automatically obtain the scapular profiles, the phase shifting method was combined with the MFPT. Four fringes were projected on the scapula and four on the reference planes. By the simple subtraction of the reference values from the scapular phase maps, the map due to the moiré fringes could be digitally obtained. After the phase decoding, the tridimensional (3D) profiles were obtained without prior information about the samples and the calculations of the scapular kinematics were carried out using dedicated software. On average, the movements of lateral rotation ranged from -1.8+/-6.1 degrees to -26.5+/-3.5 degrees; the protraction from 28.4+/-4.7 degrees to 27.7+/-6.8 degrees, and the posterior tilt from -6.4+/-7.8 degrees to -21.7+/-6.1 degrees, during the arm elevation in the scapular plane performed by six healthy subjects. For the test-retest reliability, the intra-class correlation coefficients ranged from 0.92 to 0.997 and the maximum estimated error was 0.8%. The MFPT allowed the scapular 3D measurements to be obtained in a digital and non-invasive manner. The main advantages compared with other existing systems were its ease in implementation, the use of standard optical components, and its possible clinical applications.