Instrumentation, implementation, and tracking errors occur during functional movement analysis. Instrumentation errors have been adequately addressed by other investigators. Implementation errors continue to be difficult to identify. Implementation and tracking errors are commonly associated with discontinuities (shifts and spikes) in target trajectory time history data. Shifts occur when the combination of cameras used to locate a target changes. Spikes occur when target images merge with other target images or with camera strobes. The purpose of this study was to develop a technique for identifying discontinuities, in order to prevent implementation errors and tracking errors from becoming errors in clinical judgement. To date, data from three walking trials were evaluated. Software was used to identify discontinuities in the data by calculating discontinuity parameters (DPs). The DP was calculated by scanning data for sample to sample changes in target translation accelerations. Each target trajectory discontinuity associated with a joint angle error larger than 20% of the normal joint range of motion (ankle > 8 degrees, knee > 12 degrees, hip > 8 degrees in the sagittal plane) was associated with a DP larger than 20m/s2. There was no obvious correlation between the magnitude of the DP and the size the joint angle error associated with the discontinuity. The largest DP measured 42m/s2 and was associated with a joint angle error of 13 degrees at the knee and 22 degrees at the hip in the leg model that was used for testing. It was determined that discontinuity parameter calculation is an excellent technique for identifying discontinuities in target trajectory data. The results of this study were presented at the North American Clinical Gait Laboratories Conference in Waterloo, Ontario, and an abstract was published in Gait and Posture during the month of June, 1995.
