The myth of the ankle centre of rotation: definitions, misconceptions and clinical implications

The ankle joint complex is a sophisticated structure whose kinematic behaviour is frequently oversimplified in both clinical and biomechanical practice. The hinge model, with a fixed axis aligned with the line joining medial and lateral malleoli, remains prevalent despite evidence of a migrating centre of rotation (COR) and three-dimensional motion. This paper addresses common misconceptions surrounding the COR and axis of rotation (AOR) at the ankle joint, clarifying their purely kinematic nature. A conceptual framework is provided, introducing mechanical notions of COR, centrode, helical axis and axode with reference to their application in the ankle joint analysis. The clinical relevance of accurate COR localisation is discussed, spanning the topics of muscles moment arm estimation and total ankle arthroplasty (TAA). Current limitations are critically reviewed, including the absence of standardised in vivo protocols and the insufficient integration of subject-specific kinematic assessment. Emerging acquisition technologies are proposed as the most promising avenue to bridge the gap between biomechanical knowledge and clinical translation, ultimately moving beyond the oversimplified single-axis model in the management of ankle pathology.