A 3D image-based measurement approach for analysing dynamic foot posture and mobility

The original contribution achieved from this research was the development of a low-cost 3D high-accuracy photogrammetric technique for measuring dynamic changes in foot anthropometry during gait. In clinical settings, the approach of determining foot mobility is achieved through measuring changes in bone landmarks between the static unloaded foot and the static loaded foot. From previous reliability assessment tests, it was found that static clinical foot mobility assessments based on the dorsum bone as a point of landmark reference provides high levels of measurement reliability. However, the relationships between these static dorsum measurement techniques have not been assessed against dynamic dorsum measurements collected during foot mobility. In this thesis, two assessment techniques based on the dorsum as a point of reference; namely the Foot Mobility Magnitude (FMM) and Arch Height Index (AHI) were compared statically and dynamically. The purpose for this was to validate these static measurements against the actual foot mobility during dynamic activities. An imaging platform was developed which consisted of 12 video cameras synchronised with force plate data to continuously capture the foot during gait while simultaneously obtaining ground reaction force information. The developed system achieved measurement accuracies within 0.3 mm with high levels of measurement precisions and insignificant random and systematic errors. From the research study, it was found that the correlation between the static and dynamic FMM measurements was insignificant, whereas significant correlations were found between the static and dynamic AHI measurements. Agreements between the static and dynamic AHI measurements were higher when the dorsum measurements were normalised to the truncated foot length (AHI 1) than normalising the dorsum measurements to the total foot length (AHI 2). Another major finding from the research was the higher measurement correlations achieved when the dynamic FMM and AHI were assessed between heel-strike and mid-stance compared to between heel-strike and active propulsion. This indicates that measuring the static FMM and AHI between 10% WB and 50% WB instead of between 10% WB and 90% WB might lend better insight in determining the behaviour of the foot dynamically. The Foot Posture Index (FPI) was used to classify foot postures and the relationship between the FPI scores and the dynamic FMM and AHI were assessed. It was found that the FPI was significantly correlated to the AHI measures but no correlation was found between the FPI and the FMM. The highest correlation was found for AHI 1 at active propulsion where the FPI predicted 48.9% of the variation of the AHI 1. The only FPI classification criteria to have a significant influence on the AHI at heel-strike, mid-stance and active-propulsion was the congruence of the MLA with the highest prediction of 66.7% of the variation in the AHI 1 at heelstrike.