A Critical Study on the Duality of Functional Knee Axes and Foot Contact

Estimating the functional knee axis (FKA) is crucial to correctly implanting a prosthesis and accessing joint kinematics. The correct estimation of the patient-specific joint axis of the knee is crucial for achieving a reliable assessment of musculoskeletal kinematics and dynamics Researchers have reported on the KFA mainly with regard to manual management of flexion-extension movements performed passively without any voluntary actions. Active touch and movement refer to what is ordinarily called touching—variations in skin stimulation caused by surfaces are altered together by motor activity variations. This fact is worth noting because it is often neglected that locomotion and its surfaces form an inseparable pair. The objective of this study was to confirm the distinction between touching and being touched. We were particularly interested in measuring the instantaneous axes of the knee (IAK) during locomotion. We propose the invariant structure of the knee as an attempt to distill a kind of higher-order simplification of a knee model relative to the enormous complexities of the biological systems of a human joint. This principle attempted to distill a kind of higher-order simplification relative to the enormous complexities of analytical anatomical objects and the practice of biomechanical engineering, which are sometimes confused.