Multistep pressure platform as a stand-alone system for gait assessment

THE MEASUREMENT of the mechanical quantities that describe human gait is approached with different instruments according to the desired accuracy and completeness of the data set. Complex measurement systems, such those based on 3-D optoelectronic instruments for body landmark tracking, are adequately exploited at only a few prominent clinical centres (GAGE, 1993; PERRY et al., 1993; SUTHERLAND and DAVIDS, 1993). Simpler systems have gained wider clinical acceptance. Among these, pressure insoles and pressure platforms (LORD, 1981; LORD et al., 1986; MITTLMEIER et al., 1991) are easy to use, and the results are readily interpreted without the need of complex analysis. Commercial versions of such systems are also available (HENNIG and NICOL, 1978). Regardless of the technology used, these devices are based on a matrix of sensors that detect the vertical component of the force, or equivalently the mean value of the pressure acting on the sensor area. Pressure platforms measure local pressure between the foot and the floor with spatial resolution given by the intersensor distance, whereas force platforms measure the vector in the space of the resultant ground reaction force. Pressure platforms (CAVANAGH and MICHIYOSHI, 1980; SIMK_rN and STOKES, 1982) usually have a small sensitive area sufficient to sustain only one foot. A consequent disadvantage is that the subject's walking is unnatural and parameters of the whole walking cycle, related to both feet simultaneously, cannot be measured. The ambulatory monitoring of gait, which entails the analysis of a large number of steps, has been performed with a few discrete transducers attached to the sole of the foot or the shoe (SOAMES et al., 1982; HENNIG et al., 1982; GROSS and BUNCH, 1988), or with insoles (PERUCHON et al., 1989; ZHU et al., 1991). Insoles have higher precision and spatial resolution than transducers. With both kinds of device it is possible to measure the stance of both feet simultaneously, and therefore the temporal parameters of the whole gait cycle, but spatial parameters cannot be measured as they require knowledge of the relative position of one foot with respect to the other. Measuring walkways (CROUSE et al., 1987; HIROKAWA and MATSUMURA, 1989; HmOKAWA, 1989; REILLY, 1991) have been constructed with the aim of analysing only the spatialtemporal parameters of gait during the whole walking cycle; they usually consist of conductive grids spaced 1 cm along both directions, and therefore they can detect only foot-floor contact. The platform proposed here is the final version of a device partially outlined previously (Lo VERDE et al., 1991). It has been conceived as a clinical system for basic gait analysis, in which simplicity of use and a thorough analysis have been satisfactorily combined. The wide size of the platform allows us to detect at least three successive footprints, and therefore it is particularly suitable for the measurement of the spatial and temporal quantities of gait. A consistent software package has been developed to compute gait parameters of potential clinical interest.