Assessing talonavicular joint rotations in three dimension
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KeywordsReference Frame Rotational Degree Joint Rotation Joint Axis Rotational Freedom
The union of the spherical talar head with the cupped shaped navicular shows the general characteristics of a ball-and-socket joint . As such, the talonavicular joint should be expected to demonstrate three rotational degrees of freedom. Yet, conventional approaches to foot motion analysis provide little opportunity to assess motion of the intrinsic foot joints. A new approach, and perspective, is adopted that permits an appreciation of the talonavicular joint that is not restricted to the confines of marker dependence or the orthogonal reference frame. Data will be presented that shows talonavicular rotation about independent axes that possess orientations that are not orthogonal to any conventional reference frame.
Data are derived from the legs of 23 non-pathological embalmed cadavers. Legs were prepared by removing all soft tissue, so that only ligamentous structures remained to sustain limb integrity. Each specimen was cycled through three mutually orthogonal driving actions (Plantarflexion-Dorsiflexion [PD], Inversion-Eversion [IE], and Medial-Lateral Rotation [ML]) while monitoring the relative positions of the talus and navicular with an active-marker tracking system The Functional Alignment method  was used to derive joint axis orientations and motion patterns for three rotational degrees of freedom. These results are summarized using the axis triangle technique .
The talonavicular joint is a true three degree of rotational freedom joint. It responds in unique ways to different driving inputs. To identify and understand these differences, it is necessary to adopt a perspective that is not limited to movements aligned with an orthogonal reference frame.
This article is published under license to BioMed Central Ltd.