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Abstract
The limitations of clinical methods for appraising foot posture are well documented.
A new measure, the Foot Posture Index is proposed, and its development and validation
described.
A four-phase development process was used: (i) to derive a series of candidate measures,
(ii) to define an appropriate scoring system, (iii) to evaluate the validity of components
and modify the instrument as appropriate, and (iv) to investigate the predictive validity
of the finalised instrument relative to static and dynamic kinematic models. Methods
included initial concurrent validation using Rose's Valgus Index, determination of
inter-item reliability, factor analysis, and benchmarking against three dimensional
kinematic models derived from electromagnetic motion tracking of the lower limb.
Thirty-six candidate components were reduced to six in the final instrument. The draft
version of the instrument predicted 59% of the variance in concurrent Valgus Index
scores and demonstrated good inter item reliability (Cronbach's alpha = 0.83). The
relevant variables from the motion tracking lower limb model predicted 58-80% of the
variance in the six components retained in the final instrument. The finalised instrument
predicted 64% of the variance in static standing posture, and 41% of the variance
in midstance posture during normal walking.
The Foot Posture Index has been subjected to thorough evaluation in the course of
its development and a final version is proposed comprising six component measures
that performed satisfactorily during the validation process. The Foot Posture Index
assessment is quick and simple to perform and allows a multiple segment, multiple
plane evaluation that offers some advantages over existing clinical measures of foot
posture.