The purpose of this study was to resolve the confusion existing in the terminology for describing foot motion, particularly the definitions of inversion and eversion. First, the definitions of foot motion used by the Japanese Association of Rehabilitation Medicine and the Japanese Orthopedic Association were compared with those used by the American Orthopaedic Foot and Ankle Society (AOFAS) and with those used by the International Society of Biomechanics (ISB), to identify agreements and differences. Next, the terminology utilized in the literature was explored by examining several major textbooks and related academic papers retrieved through a search of the PubMed medical literature database. In the definitions of AOFAS and ISB, inversion and eversion, which correspond to triplane motions in the definition used in Japan, were regarded as motions in the coronal plane. Terminology in the textbooks was very diverse. Of the 141 academic papers explored, 92 papers (66%) regarded inversion/eversion as coronal plane motion, and 4 papers (3%) regarded it as a triplane motion. In the remaining 43 papers (31%), the definition was unspecified. In academic articles addressing foot motions, to avoid confusion in terminology, the definitions of inversion and eversion need to be specified.
