Recently, many mathematical descriptors were proposed to quantify 3D motions of the foot and ankle complex. However, since the ranges of rotation in foot joints are rather small, the reliability of these kinematic assessments is questionable. Particularly, achievement of acceptable results for clinical decision makings demands to extract repeatable features. In this study, repeatability of kinematics assessment of multi-segment foot by means of different mathematical descriptors was investigated. 25 tiny markers were mounted on dominant anatomical landmarks of the foot and ankle complex. Six young healthy subjects were asked to walk over a forceplate surrounded by six infra-red cameras. Marker trajectories were captured during one stance phase and several trials per subject were recorded. Foot and ankle complex was considered as six rigid segments:
Shank, Hindfoot, Mid-foot, Medial forefoot Lateral forefoot Toes. 3D angles between each pair of segments (i.e., 1~2, 2~3, 3~4, 3~5 and 4~6) were calculated based on three common mathematical descriptors:
helical angle, joint coordinate system and projection angles. Then, the coefficient of multiple correlations (CMC) was used to estimate the degree of similarity among joint angle patterns for intra-subject and inter-subjects trials. It was observed that the three angle calculation methods had comparable repeatability for both intra-subject and inter-subjects kinematics. No significant difference among their repeatability was noticed. Most of angles showed good pattern repeatability intra-subject and acceptable pattern repeatability inter-subjects. In conclusion, all three calculation methods for foot joint angles can be reliably applied. Further studies enrolling patients with foot and ankle pathology are necessary to investigate the relevance of these measurements for clinical evaluations.
