Reliability of a Global Gait Symmetry Index Based on Linear Joint Displacements

Gait symmetry is commonly used as an informal measure to assess functional gait recovery. As other outcome measures used for the evaluation of clinical change over time, gait symmetry indices must be reliable. However, studies assessing the reliability of symmetry indices are scarce and focused on discrete and local indices (i.e., peak joint angle, step length), which fail to assess overall gait symmetry. On the other hand, the repeatability of global symmetry indices (using multiple continuous waveforms) based on joint angles may be hampered by the sensitivity of these variables to marker placement imprecision. The aim of this study is to evaluate the test-retest intra-rater reliability and measurement error of an alternative global symmetry index. Two 3D gait analyses were performed on separate days (a week interval) on twenty-three healthy adults. Reliability and measurement error were assessed by calculating the intraclass correlation coefficient and the 95% limits of agreement, standard error of measurement and smallest detectable change, respectively. The new symmetry index presented acceptable results in terms of reliability (ICC = 0.71, 95% CI 0.33-0.88) and measurement error (95% LOA between -30.2% and 29.1%, SEM = 10.7% and SDC = 29.7%), thus being a more promising tool to assess overall gait symmetry.