Influence of marker models on ankle kinematics in persons with partial foot amputation: An investigation using a mechanical model

Previous studies have found that ankle dorsiflexion increases in persons with partial foot amputation walking shod or in "below-ankle" devices compared with walking barefoot. However, a logical biomechanical explanation for these findings has not been offered. The purpose of this project was to determine whether marker location might explain the exaggerated dorsiflexion reported in the literature and, if so, whether more accurate data could be obtained with a different marker set. An articulated mechanical model of the shank and partial foot residuum was constructed with a potentiometer located within the mechanical ankle joint. Ankle angles measured with the calibrated potentiometer were compared with those obtained with both the Helen Hayes marker set and an alternative "residual end" marker set. Results indicated that both marker sets provided accurate and comparable measures at the metatarsophalangeal and transmetatarsal levels. At the Lisfranc level, the Helen Hayes marker set overestimated the ankle angles, primarily because of deformation of the prosthetic forefoot. These results confirm that the choice of kinematic model does influence measurements of ankle motion in persons with partial foot amputation and that the residual end marker set more accurately measures ankle motion at the Lisfranc level.