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Foot Biomechanics

Foot modelling for gait analysis

Julie Stebbins, Adward Paik, Tim Theologis

oxford_foot_modelThe foot and ankle jointly provide the interface between the body and the supporting surface during locomotion. In addition to supporting body weight, they must accommodate a variety of internal and external forces reliably over the course of a lifetime. Clinical problems with the foot and ankle range from those present at birth (e.g. clubfoot), to those due to injury (e.g. metatarsal fracture), to those related to aging (e.g. adult acquired flatfoot). Detailed study of the dynamic behaviour of the foot and ankle complex is complicated by the large number of bones and joints involved and the difficulty in measuring the individual joint motions. Tracking the motion of multiple foot segments with skin-mounted markers has been possible in recent years, but the number of segments tracked is inevitably small (~3) compared to the number of bones involved (24+).  We now have several years of research and clinical experience working with our own multi-segment foot model (the Oxford Foot Model, as implemented in Vicon Nexus software).

The objective of our current research in this area is to improve the Oxford Foot Model and assessment of foot biomechanics generally through integration of motion capture, pressure measurement under the foot, and imaging techniques. Each of these methods is currently used in isolation, but the integration of these techniques should provide a more detailed and accurate assessment by simultaneously recording both abnormal motion as well as loading of the foot. The expected outcome of our work is a clinically relevant, accurate and detailed method for routine assessment of foot deformity in a dynamic context. This will allow comprehensive information regarding the foot to be accessible to clinicians, improving treatment planning and optimising outcomes. We have also started to look into in-shoe foot motion tracking.

Flatfoot

Catriona Kerr, Alpesh Kothari, Julie Stebbins, Tim Theologis, Julia Schnabel

plantar_pressureOf the many clinical problems affecting the foot and ankle, flatfoot is one of the more subtle and challenging. It is characterised by partial or complete collapse of the medial longitudinal arch of the foot. The arch can either be flattened at all times, or only when the foot supports weight (known as 'flexible flatfoot'). All children are born with flat feet, and most, but not all, develop an arch by about age five. Treatment of feet which are clearly flat because they are deformed or injured is not controversial, but there is major uncertainty about whether a flat foot showing no clinical signs should be treated, just in case it should lead to pain, dysfunction, or arthritis somewhere in the lower limb later in life due to abnormal motion and loading over the course of several decades.

Flexible flatfeet are typically assessed and monitored clinically using basic observational tests, such as heel lifts/standing-on-toes to induce dorsiflexion of the hallux and to raise the arch, along with scoring systems for standing foot posture, such as the Foot Posture Index. Footprints and plantar pressure maps, quantified by various arch indices, are also used. Gait or video analysis, where available, may be undertaken. Our projects in this area are focussed on the condition flexible flatfoot in children and how a foot diagnosed as flat in a static condition behaves in a dynamic situation such as walking. We use kinematic, force, plantar pressure, and muscle activity measurements.

Morphology of the bones of the foot

talus_calcaneus_meshThe talus bone in the foot has a very complex shape, mainly because it articulates with several other bones: with the tibia and fibula to form the talocrural joint, with the calcaneus to form the subtalar joint, and with the navicular to form talonavicular joint. It is hypothesized that, in the adult, the shape of the talus (its morphology) is a result of the loads applied to it during growth and to the need for the talus to be mobile and also to accommodate the growth of the bones around it. One study has shown that in children the shape and orientation of three talar articular facets change over time and that certain principal components related to their shape significantly increased with body weight. This project is appling the canonical sampling methods used in the study of juvenile talus shape to analyse the shapes of talus bones in CT scans of adult feet. The principal moments of inertia of the talus and the bones surrounding it are also of interest.