Comparison of distinctive gait variables using two different biomechanical models for ankle joint kinematics

Gait analysis is an important instrument to investigate foot and ankle biomechanics in the field of footwear design. Results of this method should be objective and comparable. The purpose of this study was to compare two different approaches to quantify ankle joint kinematics: Functionally determined joint centres/axes (FA) versus a predictive model (PA). A single comprehensive marker set was defined. Twenty-two subjects were analysed, and distinctive gait variables were averaged across five trials. Agreement between methods was quantified according to Bland & Altman (Bland and Altman 1986. Lancet, i (8476), 307). Outcome variables differed remarkably between FA and PA at the talocrural (2-9°) and subtalar joints (1-6°). Considerable differences between variables describing motion of the ankle joint complex were primarily related to the use of different rotational axes and definitions of foot segments. This should be considered when studies using different foot models are compared.