Comparison of unisegment and multisegment foot models in ankle biomechanics and distal foot power calculations in individuals with a partial foot amputation

Multisegment foot models (MFMs) provide a more detailed assessment of foot biomechanics than conventional unisegment foot models (UFMs), yet their added value in individuals with a partial foot amputation remains unclear. The aim of this study was to compare the modified Oxford MFM to a conventional UFM during the stance phase of walking in individuals with a partial foot amputation. Fourteen adults with toe(s) or ray(s) amputation underwent an instrumented gait analysis using force plates and a three-dimensional motion capture system. Joint angles, moments and power were calculated using inverse dynamics and compared for each individual percentage of the stance phase using one-dimensional statistical parametric mapping. Greater ankle plantarflexion angles across the entire stance phase and greater ankle abduction angles during midstance were observed with the UFM compared with the MFM. Conversely, smaller ankle plantarflexion, inversion, and abduction moments, as well as smaller total support moments across most of the stance phase were observed with the UFM compared with the MFM. Smaller ankle and distal foot power absorption and generation during most of the stance phase, and greater distal foot power generation during pre-swing were observed with the UFM. These findings suggest that modeling the foot as a single rigid segment may alter the interpretation of foot and ankle biomechanics in individuals with a partial foot amputation by alternatively estimating intra-foot structures contribution to propulsion. The MFM may provide a distinct representation of energy restitution, supporting its use for clinical measurement and the assessment of interventions specifically targeting forefoot mechanics.